Method for Producing Oligomer and/or Monomer by Degrading Biodegradable Resin

ABSTRACT

An object of the present invention is to provide a method for efficiently producing an oligomer or a monomer by degrading a biodegradable resin using an enzyme, so that the oligomer or the monomer can be recovered. 
     The present invention provides a method for producing an oligomer and/or a monomer by degrading a biodegradable resin in a degradation liquid containing a biodegradation enzyme, a buffer agent, an organic solvent, and water. In this method, the SP value of the organic solvent is less than 8.5 or more than 11.5, and the percentage content of the organic solvent (by volume) in the degradation liquid is higher than 1% and lower than 15%. In the method for producing an oligomer or a monomer, the degradation percentage of the biodegradable resin is low, and deposits of aggregates of the oligomer and/or the monomer are few, so that the recovery percentage is high.

TECHNICAL FIELD

The present invention relates to a method for producing an oligomerand/or a monomer by enzymatically degrading a biodegradable resin, amethod for efficiently degrading a readily degradable resin composition,and a degradation liquid.

BACKGROUND ART

Currently, packaging container disposal is at issue. Incinerationdisposal as in the case of general-purpose resins results in emission ofcarbon dioxide directly to the environment, and hence is not a goodmethod. Methods of degradation by microorganisms present in theenvironment, such as landfill disposal, can be expected to reduceaddition to the environment. However, such methods take time, and it isdifficult to secure land therefor.

Meanwhile, there is proposed a method in which a molded article or thelike made of a biodegradable resin is degraded by using an enzyme (seePatent Document 1). In addition, there is proposed a method fordepolymerizing polylactic acid to produce oligomers mainly composed ofrepolymerizable cyclic compounds (see Patent Document 2).

Meanwhile, biodegradable resin compositions such as biodegradablepolylactic acid-based resin compositions have been proposed as packagingmaterials. In general, a packaging container or the like using such abiodegradable resin composition is degraded sequentially from thesurface of the container, and complete degradation of the entirecontainer requires a considerable time. Moreover, since the degradationrate of a resin is affected by internal structures of the resin such asthe crystallinity of the resin and the molecular orientation therein,there is a problem that the container has some part easy to degrade, buthas other part difficult to degrade. In this respect, variousbiodegradable resin compositions have been developed recently in orderto solve these problems. For example, there is reported a readilydegradable resin composition with a biodegradability improved byblending an aliphatic polyester which releases an acid upon hydrolysis(Patent Document 3).

Patent Document 1: Published Japanese Translation of PCT InternationalApplication No. 2001-512504

Patent Document 2: International Patent Application Publication No.WO2004/013217

Patent Document 3: International Patent Application Publication No.WO2008-038648

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

When, however, a biodegradable resin is degraded by using an enzyme, theenzyme and oligomers and/or a monomer produced by the degradation formaggregates, which eventually makes it difficult to recover the oligomersand/or the monomer. In addition, since the aggregates are not dissolvedagain, the oligomers and/or the monomer cannot be recovered. Moreover,in the method for depolymerizing polylactic acid to produce oligomersmainly composed of repolymerizable cyclic products, the oligomers cannotbe recovered in a high yield because of the low water content in thereaction system. Accordingly, a first object of the present invention isto provide a method for efficiently producing an oligomer and/or amonomer without production of such aggregates, and to provide a methodcapable of recovering the oligomer and/or the monomer.

In addition, it has been found that when the readily degradable resincomposition containing the aliphatic polyester which releases an acidupon hydrolysis as described above is enzymatically degraded in adegradation liquid, the degradation rate decreases with time.Accordingly, a second object of the present invention is to provide amethod for more efficiently degrading a readily degradable resincomposition containing an aliphatic polyester which releases an acidupon hydrolysis.

Moreover, it has been found that when a readily degradable resincomposition containing an aliphatic polyester which releases an acidupon hydrolysis as described above is enzymatically degraded in adegradation liquid, the degrading rate decreases because of thefollowing reasons. Specifically, the acid is released from the readilydegradable resin composition with time, and hence the pH of thedegradation liquid is lowered, which leads to decrease in activity ofthe enzymatic degradation. Accordingly, a third object of the presentinvention is to provide a method for more efficiently degrading areadily degradable resin composition containing an aliphatic polyesterwhich releases an acid upon hydrolysis.

Means for Solving the Problems

Regarding the above-described first object, the present inventionprovides a method for producing an oligomer and/or a monomer, comprisingdegrading a biodegradable resin in a degradation liquid containing abiodegradation enzyme, a buffer agent, an organic solvent, and water,wherein the organic solvent has an SP value of less than 8.5 or morethan 11.5, and a percentage content (by volume) of the organic solventin the degradation liquid is higher than 1% and lower than 15%.

Regarding the above-described second object, the inventors of thepresent application have found that when the readily degradable resincomposition is degraded in a degradation liquid, the acid catalyst isreleased with time, which results in a low pH of the degradation liquid,and also have found that under such a condition, the activity of thedegradation enzyme for the biodegradable resin cannot be exhibitedsufficiently. Meanwhile, the inventors have also found that, even in astate where the pH of the degradation liquid is increased, the action ofthe acidic catalysis of the acid released from the readily degradableresin composition cannot be obtained sufficiently, although thedegradation activity of the degradation enzyme is exhibited. In thisrespect, the inventors have found that, in a case where the readilydegradable resin composition containing an aliphatic polyester whichreleases an acid upon hydrolysis is enzymatically degraded, it ispossible to efficiently degrade the readily degradable resin compositionby degrading the readily degradable resin composition in an enzymedegradation liquid which is under conditions which make it possible tomaintain a pH at which both the degradation action of the acid and thedegradation action of the degradation enzyme are simultaneouslysufficiently exhibited. These findings have led to completion of thepresent invention.

Specifically, the present invention provides a method for degrading areadily degradable resin composition comprising an aliphatic polyester(A) which is biodegradable, and an aliphatic polyester (B′) whichreleases an acid upon hydrolysis and which is biodegradable at a higherdegradation rate than that of the aliphatic polyester (A), the methodcomprising: (a) a step of specifying a maximum activity pH value atwhich a degradation activity value of a hydrolase, when used to degradea simple polymer of the aliphatic polyester (A) alone in a buffersolution, is maximized; (b) a step of determining an active pH range inwhich the degradation activity value is not less than 30% of thedegradation activity value at the maximum activity pH value; and (c) astep of degrading the readily degradable resin composition in an enzymereaction liquid containing the hydrolase, and having a pH which iswithin the active pH range and which is less than 8.0, wherein the pH ofthe enzyme reaction liquid is maintained within the active pH range andat less than 8.0 in the degradation step.

Regarding the above-described third object, the inventors of the presentapplication have found that when the readily degradable resincomposition is degraded in a degradation liquid, the acid catalyst isreleased with time, which results in a low pH of the degradation liquid,and also have found that under such a condition, the activity of thedegradation enzyme for the biodegradable resin cannot be exhibitedsufficiently. Meanwhile, the inventors have also found that, even in astate where the pH of the degradation liquid is increased, the action ofthe acidic catalysis of the acid released from the readily degradableresin composition cannot be obtained sufficiently, although thedegradation activity of the degradation enzyme is exhibited. In thisrespect, the inventors of the present application have found that, byadding, an acid neutralizing agent incompatible with the degradationenzyme to the hydrolase for degrading the readily degradable resincomposition, it is possible to maintain a pH at which both thedegradation action of the acid and the degradation action of thedegradation enzyme can be simultaneously sufficiently exhibited. Thesefindings have led to completion of the present invention.

Specifically, the present invention provides a degradation liquid fordegrading a readily degradable resin composition comprising an aliphaticpolyester (A) which is biodegradable, and an aliphatic polyester (B′)which releases an acid upon hydrolysis and which is biodegradable at ahigher degradation rate than that of the aliphatic polyester (A),wherein

-   -   the degradation liquid is a liquid mixture containing an enzyme        reaction liquid, and an acid neutralizing agent incompatible        with the enzyme reaction liquid, and preferably    -   1. the acid neutralizing agent is calcium carbonate or chitosan,        and/or    -   2. a hydrolase is protease, cutinase, cellulase, or lipase.

Moreover, the present invention provides a method for degrading areadily degradable resin composition comprising an aliphatic polyester(A) which is biodegradable, and an aliphatic polyester (B′) whichreleases an acid upon hydrolysis and which is biodegradable at a higherdegradation rate than that of the aliphatic polyester (A), the methodcomprising degrading the readily degradable resin composition in anenzyme reaction liquid containing a degradation enzyme, and an acidneutralizing agent incompatible with the enzyme reaction liquid, andpreferably

-   -   1. during the enzyme reaction, the pH of the enzyme reaction        liquid is maintained within an active pH range determined by the        following steps (a′) to (b′) and at less than 8.0: and/or    -   (a′) a step of specifying a maximum activity pH value at which a        degradation activity value of the degradation enzyme, when use        to degrade a simple polymer of the aliphatic polyester (A) alone        in a buffer solution, is maximized;    -   (b′) a step of determining an active pH range in which the        degradation activity value is not less than 30% of the        degradation activity value at the maximum activity pH value;        and/or    -   2. the acid released from the aliphatic polyester (B′) is oxalic        acid, maleic acid, or glycolic acid; and/or    -   3. the readily degradable resin composition is obtained by        dispersing a polyoxalate in a polylactic acid-based resin.

EFFECTS OF THE INVENTION

The method for producing an oligomer and/or a monomer of the presentinvention makes it possible to efficiently produce an oligomer and/or amonomer at a high degradation percentage of the biodegradable resin,while the production of deposits of aggregates is suppressed during thedegradation of the biodegradable resin. In addition, the obtainedoligomer can be degraded to the monomer, and the monomer can berepolymerized.

In addition, the degradation method of the present invention makes itpossible to improve the degrading rate of the readily degradable resincomposition in the degradation liquid because of the degradation effectsof both the acid and the degradation enzyme.

BEST MODES FOR CARRYING OUT THE INVENTION

1. Regarding Method for Producing Oligomer and/or Monomer

In a method for producing an oligomer and/or a monomer of the presentinvention, a biodegradable resin or a formed body containing thebiodegradable resin is degraded in a degradation liquid containing abiodegradation enzyme, a buffer agent, an organic solvent, and water.

The oligomer herein refers to a polymeric substance in which monomersare bonded to each other, and examples thereof include a dimer, atrimer, a tetramer, and the like. In addition, the oligomer and/or themonomer may be linear or may have side chains.

The biodegradable resin may be any resin as long as the resin isbiodegradable, and examples of the biodegradable resin includechemically synthesized resins, microorganism-based resins, naturalproduct-based resins, and the like. Specific examples thereof includealiphatic polyesters, polyvinyl alcohol (PVA), celluloses, and the like.Examples of the aliphatic polyesters include polylactic acid (PLA)resins, derivatives thereof, polybutylene succinate (PBS) resins,derivatives thereof, polycaprolactone (PCL), polyhydroxybutyrate (PHB),derivatives thereof, polyethylene adipate (PEA), polyglycolic acid(PGA), polytetramethylene adipate, condensation products of a diol and adicarboxylic acid, and the like. Examples of the celluloses includemethyl cellulose, ethyl cellulose, acetyl cellulose, and the like.Moreover, the biodegradable resin may be a modified product or acopolymer of the above-described biodegradable resins, and also may be amixture of the above-described biodegradable resins, or a mixture of theabove-described biodegradable resin with a general-purpose chemicalresin, or an additive. Here, examples of the additive include aplasticizer, a heat stabilizer, a light stabilizer, an antioxidant, anultraviolet absorber, a fire retardant, a coloring agent, a pigment, afiller, an inorganic bulking agent, a mold release agent, an antistaticagent, a flavor and/or fragrance, a lubricant, a foaming agent, anantibacterial/antifungal agent, a nucleating agent, and the like.Examples of a polymer blended with the biodegradable resin includecelluloses, chitin, glycogen, chitosan, polyamino acids, starch, and thelike.

Preferably, the biodegradable resin contains a degradation accelerator.Those skilled in the art can select as appropriate an acid capable ofpromoting the degradation of the biodegradable resin, and can use theacid for the degradation accelerator. For example, an acid can be usedwhich releases, upon hydrolysis, an acid showing a pH of 4 or less, forexample, an acid showing a pH of 3 or less, an acid showing a pH of 2 orless, for example, an acid showing a pH of 1.5 or less, a pH of 1.3 orless, or a pH of 1.0 or less when dissolved in water at a concentrationof 0.005 g/ml. Specific examples of the acid include oxalic acid (pH1.6), and maleic acid and glycolic acid (pH 2.5). Examples of such adegradation accelerator include polyethylene oxalate, poly (neopentyl)oxalate (PNOx), polyethylene maleate, polyglycolic acid, and the like.Preferred degradation accelerators are polyethylene oxalate andpolyglycolic acid. These degradation accelerators may be used as acopolymer, alone, or in combination of two or more kinds.

Examples of other components forming the degradation accelerator or thecopolymer include polyvalent alcohols such as ethylene glycol, propyleneglycol, butanediol, octanediol, dodecanediol, neopentyl glycol,glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethyleneglycol; dicarboxylic acids such as succinic acid, adipic acid, sebacicacid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylicacid, terephthalic acid, isophthalic acid, and anthracene dicarboxylicacid; hydroxy carboxylic acids such as L-lactic acid, D-lactic acid,hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid,hydroxycaproic acid, mandelic acid, and hydroxybenzoic acid; lactonessuch as glycolide, caprolactone, butyrolactone, valerolactone,propiolactone, and undecalactone; and the like.

In the present description, a polyoxalate means a polymer which may be ahomopolymer, a copolymer, or a polymer blend in which oxalic acid ispolymerized as at least one monomer.

The content of the degradation accelerator in the biodegradable resin ispreferably 1 to 30% by weight, and more preferably 2 to 20% by weight inconsideration of mechanical properties and processability.

The biodegradable resin is preferably a polylactic acid resin. Thepolylactic acid resin is not particularly limited, as long as thepolylactic acid resin is a polyester resin obtainable by polymerizinglactic acid. The polylactic acid resin may be a homopolymer, acopolymer, a polymer blend, or the like of polylactic acid.

Examples of components forming the polylactic acid and the copolymerinclude polyvalent alcohols such as ethylene glycol, propylene glycol,butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin,pentaerythritol, sorbitan, bisphenol A, and polyethylene glycol;dicarboxylic acids such as succinic acid, adipic acid, sebacic acid,glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid,terephthalic acid, isophthalic acid, and anthracene dicarboxylic acid;hydroxycarboxylic acids such as glycolic acid, L-lactic acid, D-lacticacid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid,hydroxycaproic acid, mandelic acid, and hydroxybenzoic acid; lactonessuch as glycolide, caprolactone, butyrolactone, valerolactone,propiolactone, and undecalactone; and the like.

Examples of the polymer blended include celluloses, chitin, glycogen,chitosan, polyamino acids, starch, and the like. Note that, whenpolylactic acid is used, the lactic acid used for the polymerization maybe any one of the L-isomer and the D-isomer, or a mixture of theL-isomer and the D-isomer.

The biodegradable resin is preferably a readily degradable resincomposition including an aliphatic polyester (A) which is biodegradable,and an aliphatic polyester (B′) which releases an acid upon hydrolysis,and which is biodegradable at a higher degradation rate than that of thealiphatic polyester (A)

The formed body of the biodegradable resin may be any formed body, aslong as the formed body is formed by a known forming method. Examples ofthe known forming method include injection molding, extrusion molding,sheet forming, and the like. The layer structure of the obtained formedbody is not limited to a single layer structure, and accordingly may bea multilayer structure.

The biodegradation enzyme contained in the degradation liquid is notparticularly limited, as long as the biodegradation enzyme is adegradation enzyme which acts on the biodegradable polymer. Moreover,the enzyme may be immobilized, but does not necessarily have to beimmobilized. Examples of the enzyme include lipase, protease, cutinase,and the like. Alternatively, microorganisms may be contained in thedegradation liquid, where an extracellular enzyme thereof is used.Culture medium components and nutrients required by the microorganismsmay be added to the degradation liquid. Those skilled in the art candetermine as appropriate the amount of the biodegradation enzyme, andcan determine the amount, for example, on the basis of an activity unitspecific to the enzyme to be used so as to match the biodegradable resinto be degraded.

Examples of the buffer agent contained in the degradation liquid includeglycine-hydrochloride buffer solutions, phosphate buffer solutions,tris-hydrochloride buffer solutions, acetate buffer solutions, citratebuffer solutions, citrate-phosphate buffer solutions, borate buffersolutions, tartrate buffer solutions, glycine-sodium hydroxide buffersolutions, and the like. Alternatively, a solid neutralization agent mayalso be used as the buffer agent, and examples thereof include calciumcarbonate, chitosan, deprotonated ion-exchange resins, and the like.Those skilled in the art can determine as appropriate the amount of thebuffer agent, and, for example, a buffer solution having a saltconcentration of 10 to 100 mM can be used.

The SP value (Hildebrand solubility parameter) of the organic solventcontained in the degradation liquid needs to be less than 8.5 or morethan 11.5. Examples of such an organic solvent include hexane (having aSP value of 7.3), cyclohexane (8.2), dimethylsulfoxide (14.4),acetonitrile (11.7), ethanol (12.7), methanol (14.4), and the like. Theorganic solvent preferably has a SP value of not more than 8.5 or notless than 11.6. More preferably, the SP value is not more than 8 or notless than 12. Further preferably, the SP value is not more than 7.5 ornot less than 12.5. When an organic solvent having an SP value withinany one of the above-described ranges is used, the degradationpercentage of the biodegradable resin is high, and the formation of theaggregates can be suppressed. The organic solvent is preferably ethanol.

The percentage content (by volume) of the organic solvent in thedegradation liquid is higher than 1% and lower than 15%. Preferably, thepercentage content of the organic solvent is 1.5% to 12%. Morepreferably, the percentage content of the organic solvent is 2% to 10%.Further preferably, the percentage content of the organic solvent is 4%to 10%. If the percentage content (by volume) of the organic solvent isnot higher than 1%, deposits of aggregates are formed in the degradationliquid, which results in reduction in recovery percentage of theoligomer or the monomer. Meanwhile a percentage content of not lowerthan 15% is not preferable because the degradation percentage of thebiodegradable resin decreases.

The percentage content (by volume) of water in the degradation liquid isnot lower than 50%. Preferably, the percentage content may be 80 to 99%.

The temperature for the degradation of the biodegradable resin in thedegradation liquid may be any, as long as the enzyme exhibits adegradation activity at the temperature. More preferably, thetemperature is 0° C. to 100° C. Further preferably the temperature is20° C. to 70° C. In addition, when the biodegradable resin contains thedegradation accelerator, the temperature can be set in furtherconsideration of temperature conditions under which the action of thedegradation accelerator is exhibited. In such a case, for example, astandard may be represented as follows: (a temperature which is 5° C.lower than the glass transition temperature of the degradationaccelerator)<the degradation temperature <the upper temperature limit ofthe enzyme activity. For example, when polyethylene oxalate is used asthe degradation accelerator, the degradation can be promoted, forexample, under a temperature condition of 37° C. Meanwhile, whenpolyglycolic acid is used as the degradation accelerator, thedegradation can be promoted, for example, at 45° C. In addition, thetime for degradation of a biodegradable resin (2 cm×2 cm, thickness: 100μm) in the degradation liquid is preferably 1 day to 10 days, and morepreferably 1 day to 7 days. Further preferably, the time is within 4days. In addition, the stirring conditions of the degradation liquid arenot particularly limited, as long as the degradation liquid is stirreduniformly.

2. Regarding Method for Degrading Readily Degradable Resin Compositionand Degradation Liquid Therefor

In the present invention, the readily degradable resin compositionincludes an aliphatic polyester (A) which is biodegradable, and analiphatic polyester (B′) which releases an acid upon hydrolysis, andwhich is biodegradable at a higher degradation rate than that of thealiphatic polyester (A). Examples of the readily degradable resincomposition include readily degradable resin compositions described inInternational Patent Application Publication No. WO2008-038648, and thelike.

Examples of the aliphatic polyester (A) which is biodegradable include apolylactic acid resin; polybutylene succinate; polycaprolactone;polyhydroxybutyrate; a polybutylene succinate/adipate copolymer; acopolymer of any of the above-described aliphatic polyesters; acopolymer of any one of the above-described aliphatic polyesters with anaromatic polyester such as polyethylene terephthalate, polyethylenenaphthalate, or polybutylene terephthalate. These polyesters may be usedalone or in combination of two or more kinds thereof.

Examples of components forming the copolymer of the aliphatic polyester(A) include polyvalent alcohols such as ethylene glycol, propyleneglycol, butanediol, octanediol, dodecanediol, neopentyl glycol,glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethyleneglycol; dicarboxylic acids such as succinic acid, adipic acid, sebacicacid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylicacid, terephthalic acid, isophthalic acid, and anthracene dicarboxylicacid; hydroxycarboxylic acids such as glycolic acid, L-lactic acid,D-lactic acid, hydroxypropionic acid, hydroxybutyric acid,hydroxyvaleric acid, hydroxycaproic acid, mandelic acid, andhydroxybenzoic acid; lactones such as glycolide, caprolactone,butyrolactone, valerolactone, propiolactone, and undecalactone; and thelike.

Examples of the polymer blended include celluloses, chitin, glycogen,chitosan, polyamino acids, starch, and the like. Note that, whenpolylactic acid is used, the lactic acid used for the polymerization maybe any of the L-isomer and the D-isomer, or a mixture of the L-isomerand the D-isomer.

Preferred examples of the aliphatic polyester (A) which is biodegradableinclude polylactic acid-based resins, polybutylene succinate, and thelike.

The molecular weight of the aliphatic polyester (A) which isbiodegradable is not particularly limited, and the weight averagemolecular weight thereof is preferably in a range from 5,000 to1,000,000, and more preferably in a range from 10,000 to 500,000 inconsideration of mechanical properties and processability during theproduction of a container or the like from the readily degradable resincomposition containing the aliphatic polyester (A).

The aliphatic polyester (B′) releases an acid upon hydrolysis, and isbiodegradable at a higher degradation rate than that of the aliphaticpolyester (A). Here, in the present description, “being biodegradable ata higher degradation rate” refers to the fact that, when a simplepolymer alone is enzymatically degraded in an aqueous solution, theamount of degradation products eluted per day (degradation rate) islarger (higher) than that of the aliphatic polyester (A), and preferablyrefers to the fact that the amount of the degradation products(degradation rate) of the single polymer is twice or more as large(high) as that of the aliphatic polyester (A). In the presentdescription, the aliphatic polyester (B′) which is biodegradable at ahigher degradation rate than that of the aliphatic polyester (A) isreferred to as a “readily degradable aliphatic polyester (B′)” for thesake of convenience.

The acid to be released is not particularly limited, as long as the acidsatisfies the above-described conditions. For example, an acid can beused which releases, upon hydrolysis, an acid showing a pH of 4 or less,for example, an acid showing a pH of 3 or less, an acid showing a pH of2 or less, for example, an acid showing a pH of 1.5 or less, a pH of 1.3or less, or a pH of 1.0 or less when dissolved in water at aconcentration of 0.005 g/ml. Specific examples thereof include oxalicacid (pH 1.6), maleic acid, maleic anhydride, glycolic acid (pH 2.5),and the like. Among these, oxalic acid, maleic acid, and glycolic acidare preferable. By use of such an aliphatic polyester (B′), thealiphatic polyester (A) is degraded rapidly. This is presumably because,when water enters and elutes the aliphatic polyester (B′), the elutedacid component hydrolyzes the aliphatic polyester (A) such as polylacticacid, causing a large number of cracks inside the aliphatic polyester(A), which in turn increases the surface area on which an enzyme acts.Not only the aliphatic polyester (B′) releases the acid upon hydrolysisto leave cracks formed in the aliphatic polyester (A), but also thealiphatic polyester (B′) itself is eluted to leave pores formed insidethe aliphatic polyester (A).

As a result, a larger number of sites on which the enzyme acts can beformed inside the aliphatic polyester (A), which can further increasethe degradation rate.

Examples of the readily degradable aliphatic polyester (B′) includepolyethylene oxalate, poly(neopentyl) oxalate (PNO_(x)), polyethylenemaleate, polyglycolic acid, and the like. These may be used as acopolymer, alone, or in combination of two or more kinds.

Examples of components forming the copolymer include polyvalent alcoholssuch as ethylene glycol, propylene glycol, butanediol, octanediol,dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan,bisphenol A, and polyethylene glycol; dicarboxylic acids such assuccinic acid, adipic acid, sebacic acid, glutaric acid,decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalicacid, isophthalic acid, and anthracene dicarboxylic acid;hydroxycarboxylic acids such as glycolic acid, L-lactic acid, D-lacticacid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid,hydroxycaproic acid, mandelic acid, and hydroxybenzoic acid; lactonessuch as glycolide, caprolactone, butyrolactone, valerolactone,propiolactone, and undecalactone; and the like. In the presentdescription, a polyoxalate means a polymer which may be a homopolymer, acopolymer, or a polymer blend in which oxalic acid is polymerized as atleast one monomer.

Among these, preferred degradation accelerators are polyoxalate andpolyglycolic acid.

The readily degradable aliphatic polyester (B′) is preferably dispersedin the aliphatic polyester (A). The enzyme can enter voids from whichthe readily degradable aliphatic polyester (B′) is eluted by degradationin water, and the enzyme in the voids acts thereon. Thus, the readilydegradable resin composition is degraded not only from the surfacethereof, but also from the inside thereof. For this reason, thedegradation rate is increased. Examples of such a readily degradableresin composition include readily degradable resin compositions eachobtained by dispersing a polyoxalate or polyglycolic acid in apolylactic acid-based resin.

Here, in order to attain a good degradation rate, the readily degradablealiphatic polyester (B′) is preferably present in the aliphaticpolyester (A) in a uniformly and finely dispersed manner. One or moremonomer components of the aliphatic polyester (A) may be polymerized inthe readily degradable aliphatic polyester (B′), in order to improve thedispersibility of the readily degradable aliphatic polyester (B′) in thealiphatic polyester (A).

Furthermore, the readily degradable aliphatic polyester (B′) ispreferably highly polarized, i.e., preferably has a high affinity forwater. Such a readily degradable aliphatic polyester (B′) has anincreased hydrolysis rate. Thus, a large number of pores are formedrapidly inside the aliphatic polyester (A), which increase the area onwhich the enzyme acts. As a result, the degradation rate of thealiphatic polyester (A) is also increased. The polarity can be indicatedby a SP value (solubility parameter) calculated by the Fedors method(Polym. Eng. Sci., 14, 147-154 (1974)), or the like. The SP value maybe, in an example case, 22.0 or more, 23.0 or more, or 24.0 or more, andis preferably 25.0 or more.

The content of the readily degradable aliphatic polyester (B′) in thereadily degradable resin composition degraded by the method of thepresent invention is preferably 1 to 30% by weight, and more preferably2 to 20% by weight in consideration of mechanical properties andprocessability during the production of a container and the like fromthe readily degradable resin composition containing the readilydegradable aliphatic polyester (B′).

The readily degradable resin composition degraded by the method of thepresent invention can be produced by uniformly mixing the biodegradablealiphatic polyester (A) and the readily degradable aliphatic polyester(B′) by an ordinary method. For example, the biodegradable aliphaticpolyester (A) and the readily degradable aliphatic polyester (B′) aresimultaneously fed to a single- or twin-screw extruder-kneader tothereby be melt-mixed, and thereafter are palletized. Thus, the readilydegradable resin composition of the present invention can be produced.The melt-extrusion temperature is generally 100 to 250° C.; however,those skilled in the art can set any melt-extrusion temperatureappropriately, in consideration of the glass transition temperatures,the melting points, and the mixing ratio of the biodegradable aliphaticpolyester (A) and the readily degradable aliphatic polyester (B′) to beused.

The readily degradable resin composition degraded by the method of thepresent invention may be blended with known additives such as aplasticizer, a heat stabilizer, a light stabilizer, an antioxidant, anultraviolet absorber, a fire retardant, a coloring agent, a pigment, afiller, a bulking agent, a mold release agent, an antistatic agent, aflavor and/or fragrance, a lubricant, a foaming agent, anantibacterial/antifungal agent, and a nucleating agent, if necessary.The readily degradable resin composition degraded by the method of thepresent invention may also be blended with a resin other than thebiodegradable aliphatic polyester (A) and than the readily degradablealiphatic polyester (B′) within a range not impairing effects of thepresent invention. For example, the readily degradable resin compositioncan be blended with water soluble resins such as polyethylene glycol andpolyvinyl alcohol, as well as polyethylene, polypropylene, anethylene-propylene copolymer, an acid modified polyolefin, anethylene-methacrylic acid copolymer, an ethylene-vinyl acetatecopolymer, an ionomer resin, polyethylene terephthalate, polybutyleneterephthalate, polyvinyl acetate, polyvinyl chloride, polystyrene, apolyester rubber, a polyamide rubber, a styrene-butadiene-styrenecopolymer, or the like. The readily degradable resin composition may beblended with a copolymer of the biodegradable aliphatic polyester (A)and the readily degradable aliphatic polyester (B′) in order to improvethe dispersibility of the readily degradable aliphatic polyester (B′).

A forming method known per se can be used to produce a container usingthe readily degradable resin composition to be degraded by the method ofthe present invention.

For example, a multilayer film, a multilayer sheet, a multilayerparison, a multilayer pipe, and the like can be molded by extrusionmolding using multiple extruders, the number of the multiple extrudersbeing equivalent to the number of kinds of the resins and using amultiple die for multilayer. Meanwhile, a multilayer preform for bottleformation can be produced by co-injection molding such as a simultaneousinjection method or a sequential injection method using multipleinjection molding machines, the number of the injection molding machinesbeing equivalent to the number of kinds of the resins. By furtherprocessing such a multilayer film, parison or preform, the containerusing the readily degradable resin composition to be used in the methodof the present invention can be obtained.

A packaging material such as a film can be used for a pouch in variousforms or for a top member of a tray or a cup. Examples of the pouchincludes three- or four-side sealed flat pouches, pouches with a gusset,standing pouches, pillow packaging bags, and the like. These pouches andbags can be produced by a known pouch or bag forming method. Meanwhile,a packaging container in a cup shape, a tray shape, or the like can beobtained by subjecting the film or the sheet to means such as vacuummolding, pressure molding, bulge forming or plug-assist molding.

An extrusion coating method or a sandwich lamination can be used toproduce a multilayer film or a multilayer sheet. Meanwhile, asingle-layer or multilayer film formed in advance can be laminated bydry lamination to produce a multilayer film or a multilayer sheet.Examples of the production method include a method in which atransparent biodegradable deposition film is dry laminated on a doublelayered co-extrusion film formed of the readily degradable resincomposition/a polylactic acid (sealant) layer; a method in which twolayers of the readily degradable resin composition/polylactic acid(sealant) are extrusion coated onto a double layered film of polylacticacid/polyglycolic acid dry-laminated on each other with an anchoringagent interposed therebetween; and the like. However, the productionmethod is not limited to these.

In addition, a bottle or a tube can be easily molded by pinching off aparison, a pipe, or a preform with a pair of split dies and then byblowing a fluid into the pinched-off parison, pipe or preform. Inaddition, an oriented blow-molded bottle and the like can be obtained asfollows. Specifically, a pipe or a preform is cooled, thereafter, heatedto an orientation temperature, and then oriented in the axial direction,while blow-oriented in the circumferential direction by a fluidpressure.

The hydrolase used in the present invention is not particularly limited,as long as the hydrolase generally degrades biodegradable resins. Thoseskilled in the art can use any degradation enzyme. Examples of such anenzyme include protease, cellulase, cutinase, lipase, and the like. Forexample, it is possible to use protease K manufactured by Wako PureChemical Industries, Ltd. or lipase CS2 of National Research Instituteof Brewing. Those skilled in the art can determine as appropriate theamount of the hydrolase, and may determine the amount, for example, onthe basis of active unit specific to the enzyme to be used so as tomatch the readily degradable resin to be degraded.

The buffer solution used in the present invention is not particularlylimited, as long as the buffer solution is a buffer solution generallyused to stabilize pH. Examples of such a buffer solution includeglycine-hydrochloride buffer solutions, phosphate buffer solutions,tris-hydrochloride buffer solutions, acetate buffer solutions, citratebuffer solutions, citrate-phosphate buffer solutions, borate buffersolutions, tartrate buffer solutions, glycine-sodium hydroxide buffersolutions, and the like. Alternatively, a solid neutralizing agent mayalso be used for the buffer solution, and examples thereof includecalcium carbonate, chitosan, deprotonated ion-exchange resins, and thelike. Those skilled in the art can determine as appropriate theconcentration of the buffer solution, and, for example, a buffersolution having a salt concentration of 10 to 100 mM can be used.

In step (a) of the present invention, a maximum activity pH value isspecified at which a degradation activity of a hydrolase in a case wherea simple polymer of the aliphatic polyester (A) alone is degraded in thebuffer solution by the hydrolase is maximized. The simple polymer of thealiphatic polyester (A) is made of the aliphatic polyester (A) alone,which is one of the components of the above-described readily degradableresin composition. One having the same shape as the readily degradableresin composition to be degraded is preferably used. Conditions such asthe amount of the degradation liquid and the temperature thereof can beset as appropriate by those skilled in the art, and are preferably setto the same as those in step (c) to be described later.

In this step, multiple experiments on the degradation of the simplepolymer of the aliphatic polyester (A) alone are conducted by usingbuffer solutions of different pH values to specify the maximum activitypH value at which the degradation activity value of the hydrolase whichdegrades the simple polymer of the aliphatic polyester (A) alone ismaximized. The degradation activity value can be determined, forexample, based on a degradation amount of the aliphatic polyester (A) ina certain period of time, and may be determined in modified mannersdepending on the mode of the degradation of the readily degradable resincomposition. Regarding the number of pH values set for the buffersolutions and the intervals of the pH values, those skilled in the artcan determine values necessary for specifying an optimal pH for thedegradation. The pHs of the buffer solutions of various pHs used in thestep do not necessarily have to cover the entire pH region, and theintervals thereof do not necessarily have to be the same. Those skilledin the art can set the values based on a peak of the degradationactivity value which is roughly estimated for an ordinary case so thatthe values can have an appropriate distribution.

In step (b) of the present invention, a pH range in which thedegradation activity value is not less than 30% of the degradationactivity value at the maximum activity pH value is determined.Generally, an enzyme activity has an optimum pH, which varies dependingon the kind of the enzyme, reaction conditions, and the like, and theactivity can be represented by a mountain-like shape with the optimum pHbeing a peak. Accordingly, it is possible to easily determine an activepH range in which an activity not less than 30% of the degradationactivity at the maximum activity pH value specified in step (a) isexhibited, by forming a graph showing change in activity of thedegradation enzyme with change in pH in step (a). Note that, in thepresent invention, it is not necessary to set a limit of the degradationactivity value in a strict manner, but those skilled in the art candetermine a value, with a certain width, necessary for degrading thereadily degradable resin composition to a desired extent in accordancewith the absolute value of the degradation activity value or thedistribution of the degradation activity.

In step (c) of the present invention, the readily degradable resincomposition (i.e., the resin composition containing both the aliphaticpolyester (A) and the aliphatic polyester (B′)) is degraded in an enzymereaction liquid containing the hydrolase and having a pH which is withinthe active pH range, and which is less than 8.0. Here, during thedegradation step, the pH of the enzyme reaction liquid is maintained ina range which is within the active pH range and which is less than 8.0.By setting the pH within the active pH range, the action of thehydrolase can be obtained sufficiently, and simultaneously by employinga pH less than 8.0, the degradation action of the acid showing a pH of2.0 or less released upon hydrolysis from the aliphatic polyester (B′)released upon hydrolysis can be obtained sufficiently. Accordingly, thedegradation actions of both the acid and the degradation enzyme canimprove the degrading rate of the readily degradable resin composition.

In this step, the pH value of the enzyme reaction liquid is maintainedunder the above-described pH conditions. Specifically, not only at thebeginning of the reaction immediately after the readily degradable resincomposition is introduced into the enzyme reaction liquid, but alsothroughout this step, i.e., for a period of time necessary for degradingthe readily degradable resin composition to a desired extent, the pH iswithin the pH range. However, deviation of the pH from theabove-described pH range for a short period of time is acceptable, andthe pH value only needs to be controlled within the range to such anextent that a period of time necessary for the degradation of thereadily degradable resin composition is secured.

A method for maintaining the pH in a range which is within the active pHrange and which is less than 8.0 is not particularly limited, and thoseskilled in the art can employ any method. For maintaining the pH, forexample, the enzyme degradation liquid may be replaced after apredetermined period of time, for example, two days or three days, haselapsed; the concentration of the buffer solution may be adjusted withina range not affecting the activity of the degradation enzyme; or aneutralizing agent such as calcium carbonate may be added to the enzymedegradation liquid.

Additionally, according to the degradation method of the presentinvention using an acid neutralizing agent incompatible with an enzymereaction liquid, a readily degradable resin composition is degraded inan enzyme reaction liquid containing a degradation enzyme, and an acidneutralizing agent incompatible with the enzyme reaction liquid, thereadily degradable resin composition including an aliphatic polyester(A) which is biodegradable, and an aliphatic polyester (B′) whichreleases an acid upon hydrolysis and which is biodegradable at a higherdegradation rate than that of the aliphatic polyester (A). Thus, thedegradation rate of the readily degradable resin composition can beimproved, and the readily degradable resin composition can be degradedefficiently in a short period of time.

Although the exact reason for this is not clarified, the following arepossible. The surface of the readily degradable resin composition isdegraded through enzymatic degradation, and the inside thereof isdegraded by the acid such as oxalic acid released upon hydrolysis. Then,the acid such as oxalic acid or lactic acid eluted to the outside fromthe readily degradable resin composition is neutralized with the acidneutralizing agent, and moreover the acid neutralizing agent does notenter the inside of the readily degradable resin composition, and thusdoes not inhibit the degradation by the acid. As a result, the initialdegradation rate is extremely high.

The degradation method of the present invention using an acidneutralizing agent incompatible with an enzyme reaction liquid ischaracterized in that the readily degradable resin composition isdegraded in an enzyme reaction liquid containing a degradation enzyme,and an acid neutralizing agent incompatible with the enzyme reactionliquid.

The degradation enzyme used in the degradation method of the presentinvention in which the acid neutralizing agent incompatible with theenzyme reaction liquid is used is not particularly limited, as long asthe degradation enzyme generally degrades biodegradable resins. Thoseskilled in the art can use any degradation enzyme. Examples of such anenzyme include protease, cellulase, cutinase, lipase, and the like. Forexample, it is possible to use protease K manufactured by Wako PureChemical Industries, Ltd. or lipase CS2 of National Research Instituteof Brewing. The amount of the enzyme added to the enzyme reaction liquidcan be determined as appropriate by those skilled in the art on thebasis of the kind of the enzyme, the amount of the film, and the like,and is not particularly limited. For example, when a powder ofTritirachium album-derived Proteinase K (manufactured by Wako PureChemical Industries, Ltd.) is used, the powder can be used in an amountof 1 to 10 μg, preferably 5 to 8 μg per milligram of the biodegradableresin to be degraded.

In the present invention, the meaning of the acid neutralizing agentincompatible with the enzyme reaction liquid include general acidneutralizing agents other than liquid neutralizing agents, and thansolid or semi-solid neutralizing agents and the like which easily andcompletely dissolve in the enzyme reaction liquid under conditionsgenerally employed for enzyme reaction in a liquid, and is notparticularly limited. Such neutralizing agents are known to thoseskilled in the art, and examples thereof include calcium carbonate,chitosan, cation exchange resins, and the like. Among these, calciumcarbonate or chitosan is preferable in the present invention.

The solubility of the acid neutralizing agent used in the presentinvention varies depending on the composition, the temperature, and thelike of the enzyme reaction liquid. However, the kind of the acidneutralizing agent is not particularly limited, as long as the acidneutralizing agent can stably maintain the pH within the enzyme activitypH range under the test conditions. In addition, the amount of theneutralizing agent can be determined as appropriate by those skilled inthe art, and is not particularly limited. The amount can be, forexample, 0.2 to 2 times, preferably 0.5 to 1.5 times the weight of afilm of the biodegradable resin to be degraded.

In addition, as described above, it is presumed that the degradationrate of the readily degradable resin used in the present invention isincreased because, when water enters and elutes the aliphatic polyester(B′), the eluted acid component hydrolyzes the aliphatic polyester (A)such as polylactic acid, causing a large number of cracks inside thealiphatic polyester (A), which in turn increase the surface area onwhich an enzyme acts. For this reason, to prevent neutralization of theacid which plays a role in the degradation inside the readily degradableresin, it is preferable to employ conditions under which theneutralizing agent does not enter the inside of cracks. By employingsuch conditions, the neutralizing agent does not inhibit the action ofthe acid which degrades the readily degradable resin inside the readilydegradable resin, whereas, only after the aliphatic polyester (B′) ofthe readily degradable resin is eluted into the enzyme reaction liquid,the neutralizing agent neutralizes the acid and forms a salt to therebyprevent the decrease in pH of the enzyme reaction liquid so that theactivity of the degradation enzyme can be exhibited to the maximumextent possible. The above-described conditions can be achieved byadjusting the particle diameter of the neutralizing agent to a certainvalue or larger in consideration of the relationship with the size ofthe cracks. For example, when the pores formed as a result ofdegradation of the aliphatic polyester (B′) are approximately 10 μm insize, the particle diameter of the neutralizing agent is preferably setto 10 μm or larger.

In the degradation method of the present invention using an acidneutralizing agent incompatible with an enzyme reaction liquid,preferably, the pH of the enzyme reaction liquid is maintained duringthe enzyme reaction in a range which is within an active pH rangedetermined by the following steps (a′) to (b′), and which is less than8.0:

-   -   (a′) a step of specifying a maximum activity pH value at which a        degradation activity value of the degradation enzyme in a case        where a simple polymer of the aliphatic polyester (A) alone is        degraded in a buffer solution by the hydrolase is maximized; and    -   (b′) a step of determining an active pH range in which the        degradation activity value is not less than 30% of the        degradation activity value at the maximum activity pH value.

In step (a), a maximum activity pH value is specified at which adegradation activity value of a hydrolase in a case where a simplepolymer of the aliphatic polyester (A) alone is degraded in a buffersolution by the hydrolase is maximized. The simple polymer of thealiphatic polyester (A) is made of the aliphatic polyester (A) alone,which is one of the components of the above-described readily degradableresin composition. One having the same shape as the readily degradableresin composition to be degraded is preferably used. Conditions such asthe amount of the degradation liquid and the temperature thereof can beset as appropriate by those skilled in the art, and are preferably setto the same as those in degrading the readily degradable resincomposition.

The buffer solution used in the present invention is not particularlylimited, as long as the buffer solution is a buffer solution generallyused to stabilize pH. Examples of such a buffer solution includeglycine-hydrochloride buffer solutions, phosphate buffer solutions,tris-hydrochloride buffer solutions, acetate buffer solutions, citratebuffer solutions, citrate-phosphate buffer solutions, borate buffersolutions, tartrate buffer solutions, glycine-sodium hydroxide buffersolutions, and the like.

In this step, multiple experiments on the degradation of the simplepolymer of the aliphatic polyester (A) alone are conducted by usingbuffer solutions of different pH values to specify the maximum activitypH value at which the degradation activity value of the degradationenzyme which degrades the simple polymer of the aliphatic polyester (A)alone is maximized. The degradation activity value can be determined,for example, based on a degradation amount of the aliphatic polyester(A) in a certain period of time, and may be determined in modifiedmanners depending on the mode of the degradation of the readilydegradable resin composition. Regarding the number of pH values set forthe buffer solutions and the intervals of the pH values, those skilledin the art can determine values necessary for specifying an optimal pHfor the degradation. The pHs of the buffer solutions of various pHs usedin this step do not necessarily have to cover the entire pH region, andthe intervals thereof do not necessarily have to be the same. Thoseskilled in the art can set the values based on a peak of the degradationactivity value which is roughly estimated for an ordinary case so thatthe values can have an appropriate distribution.

In step (b′), a pH range in which the degradation activity value is notless than 30% of the degradation activity value at the maximum activitypH value is determined. Generally, an enzyme activity has an optimum pH,which varies depending on the kind of the enzyme, reaction conditions,and the like, and the activity can be represented by a mountain-likeshape with the optimum pH being a peak. Accordingly, it is possible toeasily determine an active pH range in which an activity not less than30% of the degradation activity value at the maximum activity pH valuespecified in step (a′) is exhibited, by forming a graph showing changein activity of the degradation enzyme with change in pH in step (a′).Note that, in the present invention, it is not necessary to set a limitof the degradation activity value in a strict manner, but those skilledin the art can determine a value, with a certain width, necessary fordegrading the readily degradable resin composition to a desired extentin accordance with the absolute value of the degradation activity valueor the distribution of the degradation activity.

In a preferred method of the present invention, by adding the acidneutralizing agent incompatible with the enzyme reaction liquid to theenzyme reaction liquid for degrading the readily degradable resincomposition (i.e., the resin composition containing both the aliphaticpolyester (A) and the aliphatic polyester (B′)), the pH thereof can becontrolled within a certain range. Here, by setting the pH within theactive pH range determined through the steps (a′) to (b′), the action ofthe hydrolase can be obtained sufficiently, and simultaneously byemploying a pH less than 8.0, the degradation action of the acid showinga pH of 2.0 or less released upon hydrolysis from the aliphaticpolyester (B′) released upon hydrolysis can be obtained sufficiently.Accordingly, the degradation actions of both the acid and thedegradation enzyme can improve the degrading rate of the readilydegradable resin composition.

In the preferred mode, the pH of the enzyme reaction liquid ismaintained under the above-described pH conditions during the enzymereaction. Specifically, not only at the beginning of the reactionimmediately after the readily degradable resin composition is introducedinto the enzyme reaction liquid, but also throughout the degradation,i.e., for a period of time necessary for degrading the readilydegradable resin composition to a desired extent, the pH is maintainedwithin the above-described pH range. However, deviation of the pH fromthe above-described pH range for a short period of time is acceptable,and the pH value only needs to be controlled within the range to such anextent that a period of time necessary for the degradation of thereadily degradable resin composition is secured.

The temperature for degradation of the readily degradable resin in thedegradation liquid may be any, as long as the enzyme and the acidreleased from the readily degradable aliphatic polyester (B′) exhibittheir degradation activities at the temperature. More preferably, thetemperature is 0 to 100° C. Further preferably, the temperature is 20°C. to 70° C. More specifically, a standard for the temperature for thedegradation is, for example, represented as follows: (a temperaturewhich is 5° C. lower than the glass transition temperature of thereadily degradable aliphatic polyester (B′))<the degradationtemperature<the upper temperature limit of the enzyme activity. Forexample, when polyethylene oxalate is used as the readily degradablealiphatic polyester (B′), the degradation can be promoted, for example,under a temperature condition of 37° C. Meanwhile, when polyglycolicacid is used as the readily degradable aliphatic polyester (B′), thedegrading can be promoted, for example, at 45° C.

According to the degradation method of the present invention, thedegradation rate of the readily degradable resin composition can beimproved by the degradation actions of both the acid and the degradationenzyme in the degradation liquid.

Hereinafter, Examples of the present invention will be described.However, the present invention is not limited thereto.

EXAMPLES

1. Examples A-1 to 12 and Comparative Example A-1 to 17 were conductedas follows.

(Pro K (Proteinase K) Enzyme Solution)

A pro K (proteinase K) enzyme solution was prepared by dissolving 20 mgof a Tritirachium album-derived proteinase K powder in 1 ml of a 0.05 MTris-HCl buffer solution (pH 8.0) containing 50 w/w % of glycerin.

(CLE Enzyme Solution)

A Cryptococcus sp. S-2-derived lipase CS2 (Japanese Patent ApplicationPublication No. 2004-73123: provided by National Research Institute ofBrewing) enzyme solution having a lipase activity of 653 U/mL was used.The lipase activity was measured by using para-nitrophenyl laurate asthe substrate. Here, 1 U of the lipase activity is defined as the amountof enzyme with which para-nitrophenol is liberated from para-nitrophenyllaurate at 1 μmol/min.

(Measurement of Glass Transition Temperature)

The glass transition temperature (Tg) was measured by using DSC 6220manufactured by Seiko Instruments Inc. (differential scanningcalorimetry). As for the measurement conditions, the measurement wasconducted in an nitrogen atmosphere at a rate of temperature rise of 10°C. per minute from 0 to 200° C. The samples used were PEOx and PEOx 20to be described later, and the amount of each sample was 5 to 10 mg.

(Synthesis of Polyethylene Oxalate (PEOx))

Into a 300-mL separable flask equipped with a mantle heater, a stirrer,a nitrogen inlet, and a condenser, 354 g (3.0 mol) of dimethyl oxalate,223.5 g (3.6 mol) of ethylene glycol, and 0.30 g of tetrabutyl titanatewere introduced. The flask was heated under nitrogen stream from 110° C.until the inside temperature reached 170° C., while methanol was beingdistilled off. Thus, the reaction was conducted for 9 hours.

At the end, 210 ml of methanol was distilled off. Thereafter, stirringwas performed for 1 hour at an inside temperature of 150° C. and at areduced pressure of 0.1 to 0.5 mmHg. After a 7-hour reaction at aninside temperature of 170° C. to 190° C., the viscosity increased, andthe product was taken out. The η inh of the synthesized product was0.12.

The solution viscosity (η inh) was measured as follows. Specifically,the synthesized polyethylene oxalate that had been vacuum-dried at 120°C. overnight was used. The polyethylene oxalate was immersed in amixture solvent of m-chlorophenol/1,2,4-trichlorobenzene=4/1 (weightratio) and dissolved thereinto at 150° C. in approximately 10 minutes toprepare a solution at a concentration of 0.4 g/dl. Thereafter, thesolution viscosity was measured at 30° C. by use of an Ubbelohdeviscometer (Unit: dl/g).

(Synthesis of Polyoxalate (PEOx 20))

The PEOx 20 was synthesized by the same method as in the above-describedsynthesis of the PEOx, except that 94.5 g (0.8 mol) of dimethyl oxalateand 38.8 g (0.2 mol) of dimethyl terephthalate were used instead of 354g (3.0 mol) of dimethyl oxalate.

GPC measurement showed that the weight average molecular weight (Mw) ofthe PEOx was 20000. The GPC used was HLC-8120 manufactured by TosohCorporation, the columns used were two TSK gel Super HM-H columns, andthe guard column used was a TSK guard column Super H-H column. Thetemperature of a column oven was set to 40° C. Chloroform was used as aneluent, and the flow rate thereof was set to 0.5 ml/min. The amount ofsample injected was 15 μl. Polystyrene dissolved in chloroform was usedas a standard. As for sample preparation, chloroform was used as asolvent with a sample concentration of 5 mg/ml, and the sample wasfiltered before use.

(Properties of PEOx and PEOx 20)

The monomer, oxalic acid, shows a pH of 1.6 at a concentration of 0.005g/ml. The PEOx releases, upon hydrolysis, oxalic acid or oxalic acidoligomers in an aqueous solution.

TABLE 1 Monomer Contents in Polyoxalate and Glass Transition Temperaturethereof Dimetyl Terephthalic Ethylene Oxalate Acid Glycol Tg (mol) (mol)(mol) (° C.) PEOx 3 0 3.6 25 PEOx 20 0.8 0.2 1.2 45

(Fabrication of Biodegradable Resin (Polylactic Acid/PEOx) Film)

Master pellets of polylactic acid (4032D manufactured by NatureWorksLLC)/polyethylene oxalate=95/5 wt % were melt blended at 200° C. byusing a twin-screw extruder (ULT Nano 05-20AG manufactured by TechnovelCorporation), and then formed into a readily degradable resincomposition film having a thickness of 100 μm by using Labo Plastomill(manufactured by Toyo Seiki Seisaku-sho, Ltd.).

(Fabrication of Biodegradable Resin (Polylactic Acid/PEOx 20) Film)

The fabrication was conducted in the same manner, except that the PEOxwas replaced with the PEOx 20.

(Fabrication of Biodegradable Resin (PBS) Film)

Polybutylene succinate (PBS) (#1001 manufactured by Showa High PolymerCo., Ltd.) pellets were melted at 200° C. for 5 minutes, and then heatedand pressed at a pressure of 50 kgf/cm2 to form a film thereof.

(Degradation Percentage)

For the degradation percentage, the initial weight of the biodegradableresin film was measured, and the weight of the biodegradable resin filmafter being degraded for one week was measured. Then, the degradationpercentage was calculated by using the following formula.

((initial weight of biodegradable resin film−weight of film afterdegradation)/initial weight of biodegradable resin film)×100=degradationpercentage (%)

(Transparency of Degradation Liquid)

The transparency of each degradation liquid in which the film wasdegraded was visually observed. A transparent degradation liquid wasevaluated as O, and a degradation liquid in which white turbidity wasobserved immediately after the degradation was evaluated as x.

(Absorbance Measurement (Turbidity Measurement))

The absorbance of each degradation liquid in which the film was degradedwas measured by using a spectrophotometer UV-160A manufactured byShimadzu Corporation at a wavelength of 660 nm.

(Preparation Method of 60 mmol/l Phosphate Buffer Solution (pH 7))

A 60 mmol/l sodium dihydrogen phosphate aqueous solution and a 60 mMdisodium hydrogen phosphate aqueous solution were mixed with each otherat a ratio of 1:1, and the pH of the mixture was adjusted to 7 with a 60mmol/l sodium dihydrogen phosphate aqueous solution.

(Method for Preparing Buffer Solution Containing Organic Solvent)

Hereinbelow, a preparation method of a buffer solution containing 4% ofethanol is described.

Ethanol was added to the above-described 60 mmol/L phosphate buffersolution to obtain an ethanol percentage content (by volume) of 4%, andthe pH was adjusted to 7 with 1 mol/l hydrochloric acid. Thus, a buffersolution containing an organic solvent was prepared. The liquid wastermed as a 4% ethanol-containing buffer solution.

(Example A-1)

A degradation liquid was prepared by mixing 10 ml of the 60 mmol/Lphosphate buffer solution (pH 7), 12 μl of the CLE enzyme solution, andethanol in such a manner that the ethanol percentage content in thedegradation liquid became 4%. Then the pH of the degradation liquid wasadjusted to 7 by adding hydrochloric acid thereto. Into a 25-ml vial,the degradation liquid and the biodegradable resin (polylacticacid/PEOx) film cut into 2 cm×2 cm (weight: 50 mg) were introduced, andshaken at 37° C. and 100 rpm for 7 days. Note that to avoid a too-muchdecrease in pH, the 7 days was divided into 2 days, 2 days, and 3 days,between which the degradation liquid was replaced.

(Example A-2)

Example A-2 was conducted in the same manner as in Example A-1, exceptthat the ethanol percentage content was set to 2%.

(Example A-3)

Example A-3 was conducted in the same manner as in Example A-1, exceptthat the ethanol percentage content was set to 7%.

(Example A-4)

Example A-4 was conducted in the same manner as in Example A-1, exceptthat the ethanol percentage content was set to 10%.

(Example A-5)

Example A-5 was conducted in the same manner as in Example A-1, exceptthat hexane was used instead of ethanol, and that the percentage contentof hexane was set to 4%.

(Example A-6)

Example A-6 was conducted in the same manner as in Example A-1, exceptthat hexane was used instead of ethanol, and that the percentage contentof hexane was set to 10%.

(Example A-7)

Example A-7 was conducted in the same manner as in Example A-1, exceptthat methanol was used instead of ethanol, and that the percentagecontent of methanol was set to 4%.

(Example A-8)

Example A-8 was conducted in the same manner as in Example A-1, exceptthat acetonitrile was used instead of ethanol, and that the percentagecontent of acetonitrile was set to 4%.

(Example A-9)

Example A-9 was conducted in the same manner as in Example A-1, exceptthat the biodegradable resin (polylactic acid/PEOx) film was replacedwith the biodegradable resin (PBS) film.

(Example A-10)

Example A-10 was conducted in the same manner as in Example A-5, exceptthat the biodegradable resin (polylactic acid/PEOx) film was replacedwith the biodegradable resin (PBS) film.

(Example A-11)

Example A-11 was conducted in the same manner as in Example A-1, exceptthat 12 μl of the pro K enzyme solution was used.

(Example A-12)

Example A-12 was conducted in the same manner as in Example A-1, exceptthat the biodegradable resin (polylactic acid/PEOx) film was replacedwith the biodegradable resin (polylactic acid/PEOx 20) film, and thatthe degradation temperature was changed to 45° C.

(Comparative Example A-1)

Comparative Example A-1 was conducted in the same manner as in ExampleA-1, except that the ethanol percentage content was set to 1%.

(Comparative Example A-2)

Comparative Example A-2 was conducted in the same manner as in ExampleA-1, except that the ethanol percentage content was set to 15%.

(Comparative Example A-3)

Comparative Example A-3 was conducted in the same manner as in ExampleA-1, except that the ethanol percentage content was set to 20%.

(Comparative Example A-4)

Comparative Example A-4 was conducted in the same manner as in ExampleA-1, except that the ethanol percentage content was set to 30%.

(Comparative Example A-5)

Comparative Example A-5 was conducted in the same manner as in ExampleA-1, except that toluene was used instead of ethanol, and that thepercentage content of toluene was set to 4%.

(Comparative Example A-6)

Comparative Example A-6 was conducted in the same manner as in ExampleA-1, except that toluene was used instead of ethanol, and that thepercentage content of toluene was set to 50%.

(Comparative Example A-7)

Comparative Example A-7 was conducted in the same manner as in ExampleA-1, except that toluene was used instead of ethanol, and that thepercentage content of toluene was set to 95%.

(Comparative Example A-8)

Comparative Example A-8 was conducted in the same manner as in ExampleA-1, except that chloroform was used instead of ethanol, and that thepercentage content of chloroform was set to 4%.

(Comparative Example A-9)

Comparative Example A-9 was conducted in the same manner as in ExampleA-1, except that ethyl acetate was used instead of ethanol, and that thepercentage content of ethyl acetate was set to 4%.

(Comparative Example A-10)

Comparative Example A-10 was conducted in the same manner as in ExampleA-1, except that isopropanol was used instead of ethanol, and that thepercentage content of isopropanol was set to 4%.

(Comparative Example A-11)

Comparative Example A-11 was conducted in the same manner as in ExampleA-1, except that dioxane was used instead of ethanol, and that thepercentage content of dioxane was set to 4%.

(Comparative Example A-12)

Comparative Example A-12 was conducted in the same manner as in ExampleA-1, except that hexane was used instead of ethanol, and that thepercentage content of hexane was set to 1%.

(Comparative Example A-13)

Comparative Example A-13 was conducted in the same manner as in ExampleA-1, except that methanol was used instead of ethanol, and that thepercentage content of methanol was set to 1%.

(Comparative Example A-14)

Comparative Example A-14 was conducted in the same manner as in ExampleA-1, except that no ethanol was added.

(Comparative Example A-15)

Comparative Example A-15 was conducted in the same manner as inComparative Example A-14, except that the biodegradable resin(polylactic acid/PEOx) film was replaced with the biodegradable resin(PBS) film.

(Comparative Example A-16)

Comparative Example A-16 was conducted in the same manner as inComparative Example A-14, except that 12 μl of the pro K enzyme solutionwas used.

(Comparative Example A-17)

Comparative Example A-17 was conducted in the same manner as inComparative Example A-14, except that the biodegradable resin(polylactic acid/PEOx) film was replaced with the biodegradable resin(polylactic acid/PEOx 20) film.

(Results)

Tables 2 and 3 show the results of the degradation percentage in oneweek and the transparency of the degradation liquid in each of ExamplesA-1 to 12 and Comparative Examples A-1 to 17.

TABLE 2 degradation degradation solvent percentage transparencytemperature biodegradable percentage SP for 1 week of degradation enzyme(° C.) resin content (%) value (%) liquid absorbance Example CLE 37polylactic ethanol 4 12.7 100 ∘ 0.010 A-1 acid/PEOx Example CLE 37polylactic ethanol 2 12.7 100 ∘ 0.040 A-2 acid/PEOx Example CLE 37polylactic ethanol 7 12.7 100 ∘ 0.004 A-3 acid/PEOx Example CLE 37polylactic ethanol 10 12.7 58.3 ∘ — A-4 acid/PEOx Example CLE 37polylactic hexane 4 7.3 100 ∘ 0.022 A-5 acid/PEOx Example CLE 37polylactic hexane 10 7.3 100 ∘ — A-6 acid/PEOx Example CLE 37 polylacticmethanol 4 14.4 100 ∘ 0.031 A-7 acid/PEOx Example CLE 37 polylacticacetonitrile 4 11.7 47.2 ∘ — A-8 acid/PEOx Example CLE 37 PBS ethanol 412.7 100 ∘ — A-9 Example CLE 37 PBS hexane 4 7.3 100 ∘ — A-10 Examplepro K 37 polylactic ethanol 4 12.7 100 ∘ — A-11 acid/PEOx Example CLE 45polylactic ethanol 4 12.7 100 ∘ 0.011 A-12 acid/PEOx 20

TABLE 3 Comparative CLE 37 polylactic ethanol 1 12.7 100 x 0.240 ExampleA-1 acid/PEOx Comparative CLE 37 polylactic ethanol 15 12.7 8 ∘ 0.004Example A-2 acid/PEOx Comparative CLE 37 polylactic ethanol 20 12.7 5 ∘— Example A-3 acid/PEOx Comparative CLE 37 polylactic ethanol 30 12.7 4∘ — Example A-4 acid/PEOx Comparative CLE 37 polylactic toluene 4 8.90.6 ∘ — Example A-5 acid/PEOx Comparative CLE 37 polylactic toluene 508.9 3.7 x — Example A-6 acid/PEOx Comparative CLE 37 polylactic toluene95 8.9 4.3 x — Example A-7 acid/PEOx Comparative CLE 37 polylacticchloroform 4 9.3 0 ∘ — Example A-8 acid/PEOx Comparative CLE 37polylactic ethyl 4 9.6 0.2 ∘ — Example A-9 acid/PEOx acetate ComparativeCLE 37 polylactic isopropanol 4 11.5 31.7 ∘ — Example A-10 acid/PEOxComparative CLE 37 polylactic dioxane 4 10 18.91 ∘ — Example A-11acid/PEOx Comparative CLE 37 polylactic hexane 1 7.3 100 x 0.120 ExampleA-12 acid/PEOx Comparative CLE 37 polylactic methanol 1 14.4 100 x 0.245Example A-13 acid/PEOx Comparative CLE 37 polylactic — — — 100 x 0.363Example A-14 acid/PEOx Comparative CLE 37 PBS — — — 100 x 0.390 ExampleA-15 Comparative pro K 37 polylactic — — — 100 x — Example A-16acid/PEOx Comparative CLE 37 polylactic — — — 50 x — Example A-17acid/PEOx 20 * Since the transparency of the degradation liquid dependson the degradation amount, the degradation liquids of ComparativeExamples in which the resin was hardly degraded were transparent.

FIG. 2 shows a HPLC chart of the degradation liquid of Example A-3. Thisindicated that lactic acid monomer and lactic acid oligomers wereproduced from the biodegradable resin (polylactic acid/PEOx).

(HPLC Measurement Conditions)

A GULLIVER series HPLC system manufactured by JASCO Corporation wasused. Analysis conditions were as follows: a 5-μm, 4.6×250-mm AtlantisdC18 column manufactured by Waters was used in a column oven kept at 40°C.; a gradient mobile phase as shown in FIG. 5 was employed by using0.5% phosphoric acid and acetonitrile at a flow rate of 1 mL/min; and 50μl of a sample was injected. UV absorption at 210 nm was used fordetection. As the standard sample, a sample obtained by purifyingL-lactic acid (manufactured by Wako Pure Chemical Industries, Ltd.) wasused.

From the results of Examples A-1 and 2 and Comparative Examples A-1, 2,and 3, it was found that a preferred amount of the organic solvent wassuch that 1%<the amount of the organic solvent<15%. It was found thatwhen the amount of the organic solvent was 1% or less, the degradationliquid became opaque, and the recovered amount of the monomer decreased,whereas when the amount of the organic solvent was 15% or more, thedegradation amount decreased extremely.

Next, FIG. 3 shows the correlation between the degradation percentageafter a four-day degradation test and the SP value. In sum, it was foundthat a preferred SP value range of the organic solvent was such that theSP value of the organic solvent<8.5, or such that 11.5<the SP value ofthe organic solvent.

(IR Analysis on White Turbid Substance)

The white turbid liquid of Comparative Example 14 was centrifuged. Thedeposits were collected, and washed with distilled water. The collectedwhite solid was dried under reduced pressure at 40° C. overnight, andsubjected to FT-IR measurement. For the FT-IR, reflection measurementwas employed (measurement frequency: 600 cm−1 to 4000 cm−1). FIG. 4shows the results.

The peak at 1735 cm−1 is due to the carbonyl groups of polylactic acidoligomers, and the peaks at 1635 cm−1 and 1540 cm−1 are due to peptidebonds in a protein (the enzyme). In other words, it was found that thewhite turbidity was formed during the enzymatic degradation becausedeposits of aggregates of polylactic acid oligomers and the enzyme wereproduced.

(Experiments on Recovery Percentage of Lactic Acid Monomer)

The following experiments were conducted on Example A-1, Example A-3,Comparative Example A-1, and Comparative Example A-14 in each of whichthe degradation percentage after one week was 100%.

The degradation residual liquids obtained until 100% of the film wasdegraded were combined. The pro K enzyme solution was added thereto at aratio of 1.2 μL/mL, and the mixture was shaken at 37° C. for one week.By using the reaction liquid and HPLC, the amount of lactic acid monomerwas determined. The recovery percentage of lactic acid monomer wascalculated as follows: the amount of lactic acid monomer/the amount ofpolylactic acid fed×100. Table 4 shows the results.

TABLE 4 recovery percentage of lactic acid monomer (%) Example A-1 100Example A-3 100 Comparative Example A-1 34 Comparative Example A-14 262. Examples B-1 to 8 and Comparative Examples B-1 to 10 were conductedas follows.

The hydrolase solutions used were prepared as follows.

Pro K (Proteinase K) Enzyme Solution

A pro K (Proteinase K) enzyme solution was prepared by dissolving 20 mgof a powder of Tritirachium album-derived Proteinase K (Wako PureChemical Industries, Ltd.) in 1 ml of a 0.05 M Tris-HCl buffer solution(pH 8.0) containing 50 w/w % of glycerin.

CLE Enzyme Solution

A Cryptococcus sp. S-2-derived lipase CS2 (Japanese Patent ApplicationPublication No. 2004-73123) enzyme solution having a lipase activity of653 U/mL provided by National Research Institute of Brewing was used.The lipase activity was measured by using para-nitrophenyl laurate asthe substrate. Here, 1 U of the lipase activity is defined as the amountof enzyme with which para-nitrophenol is liberated from para-nitrophenyl laurate at 1 μmol/min.

(Measurement of Glass Transition Temperature)

The glass transition temperature (Tg) was measured by using DSC 6220manufactured by Seiko Instruments Inc. (differential scanningcalorimetry). As for measurement conditions, the measurement wasconducted in a nitrogen atmosphere at a rate of temperature rise of 10°C./min from 0 to 200° C. The samples used were PEOx and PEOx 20 to bedescribed later, and the amount of each sample was 5 to 10 mg.

Synthesis of Polyethylene Oxalate (PEOx) (Aliphatic Polyester (B′))

Into a 300-mL separable flask equipped with a mantle heater, a stirrer,a nitrogen inlet, and a condenser, 354 g (3.0 mol) of dimethyl oxalate,223.5 g (3.6 mol) of ethylene glycol, and 0.30 g of tetrabutyl titanatewere introduced. The flask was heated under nitrogen stream from 110° C.until the inside temperature reached 170° C., while methanol was beingdistilled off. Thus, the reaction was conducted for 9 hours. At the end,210 ml of methanol was distilled off. Thereafter, stirring was performedfor 1 hour at an inside temperature of 150° C. and at a reduced pressureof 0.1 to 0.5 mmHg. After a 7-hour reaction at an inside temperature of170° C. to 190° C., the viscosity increased, and the product was takenout. The η inh of the synthesized product was 0.12.

The solution viscosity (η inh) was measured as follows. Specifically,the synthesized polyethylene oxalate that had been vacuum-dried at 120°C. overnight was used. The polyethylene oxalate was immersed in amixture solvent of m-chlorophenol/1,2,4-trichlorobenzene=4/1 (weightratio) and dissolved thereinto at 150° C. in approximately 10 minutes toprepare a solution at a concentration of 0.4 g/dl. Thereafter, thesolution viscosity was measured at 30° C. by use of an Ubbelohdeviscometer (Unit: dl/g).

Synthesis of Polyoxalate (PEOx 20))

The polyoxalate (PEOx 20) was synthesized by the same method as in theabove-described synthesis of PEOx, except that 94.5 g (0.8 mol) ofdimethyl oxalate and 38.8 g (0.2 mol) of dimethyl terephthalate wereused instead of 354 g (3.0 mol) of dimethyl oxalate.

GPC measurement showed that the weight average molecular weight (Mw) ofthe PEOx 20 was 20000. The GPC used was HLC-8120 manufactured by TosohCorporation, the columns used were two TSK gel Super HM-H columns, andthe guard column used was a TSK guard column Super H-H column. Thetemperature of a column oven was set to 40° C. Chloroform was used as aneluent, and the flow rate thereof was set to 0.5 ml/min. The amount ofsample injected was 15 μl. Polystyrene dissolved in chloroform was usedas a standard. As for sample preparation, chloroform was used as asolvent with a sample concentration of 5 mg/ml, and the sample wasfiltered before use.

(Properties of PEOx and PEOx 20)

The monomer, oxalic acid, shows a pH of 1.6 at a concentration of 0.005g/ml. The PEOx and the PEOx 20 release, upon hydrolysis, oxalic acid oroxalic acid oligomers in an aqueous solution.

Monomer Content and Glass Transition Temperature of Polyoxalate

dimethyl terephthalic oxalate acid ethylene glycol Tg (mol) (mol) (mol)(° C.) PEOx 3 0 3.6 25 PEOx 20 0.8 0.2 1.2 45

Fabrication of Readily Degradable Resin Composition Film (AliphaticPolyester (A) +Aliphatic Polyester (B′))

Master pellets of polylactic acid (manufactured by NatureWorks LLC)/PEOxor PEOx 20=95/5 mass % were prepared by using a twin-screw extruder(manufactured by Technovel Corporation) at a melt blending temperatureof 200° C. The obtained pellets were formed into a 100-μm readilydegradable resin composition film by using Labo Plastomill (manufacturedby Toyo Seiki Seisaku-sho, Ltd.) at a film formation temperature of 200°C.

(Example B-1) (a) Measurement of Enzyme Activity of Protease onBiodegradable Film (Simple Polymer of Aliphatic Polyester (A) Component)

Into each of 60 mM phosphate buffer solutions (11 kinds in a pH range of4.7 to 9.0) which were each 10 ml in volume, and which were prepared asdegradation liquids by adding 12 μl of the pro K enzyme solutionthereto, the polylactic acid film (having a thickness of 100 μm) cutinto 2 cm×2 cm (45 mg) was immersed, and the mixture was shaken at 37°C. and 100 rpm for 4 days. The degradation amount (mg) after 4 days wasemployed as a film degradation activity value. Here, the degradationamount after 4 days was a value represented as follows: the film weight(mg) at the beginning of the degradation−the film weight (mg) after 4days. In addition, for the film weight measurement, values obtained bymeasurement after drying the film in a dryer at 45° C. overnight wereemployed. The film degradation activities in the phosphate buffersolutions with the various pHs were as follows.

TABLE 5 pH 4.7 5.5 6.0 6.5 7.0 7.2 7.5 7.8 8.0 8.5 9.0 activity 1.6 5.099.13 7.15 3.59 3.15 2.34 2.33 2.57 2.21 2.08

(b) Specifying Active pH Range

As can be seen from Table 1 above and FIG. 6 in which the contentsthereof are illustrated, the maximum activity value of the protease onthe polylactic acid film was 9.13 which was obtained when the 60 mMphosphate buffer solution of pH 6.0 was used. A range of pH 5.0 to pH7.2 in which the activity value was not less than 2.7, which was notless than 30% of the maximum activity value, was determined as theactive pH range for use of the protease.

(c) Degradation of Readily Degradable Resin Composition (ResinComposition Containing Aliphatic Polyester (A) and Aliphatic Polyester(B′))

Into 10 ml of a 60 mM phosphate buffer solution of pH 7.2 prepared as adegradation liquid by adding 12 μl of the pro K enzyme solution, thereadily degradable resin composition film {the aliphatic polyester (B′)was the PEOx} cut into 2 cm×2 cm (weight: 45 mg) was immersed, and themixture was shaken at 37° C. and 100 rpm for 7 days. To avoid a decreasein pH, the 7 days was divided into 2 days, 2 days, and 3 days, betweenwhich the degradation liquid was replaced.

(Example B-2)

Example B-2 was conducted under the same conditions as those employed inExample B-1, except that a 60 mM phosphate buffer solution of pH 7.0 wasused in the step (C) of Example 1. (Since the same readily degradableresin composition as Example 1 was used, the active pH range was thesame, namely, pH 5.0 to pH 7.2.)

(Example B-3)

Example B-3 was conducted under the same conditions as those employed inExample B-1, except that a 60 mM phosphate buffer solution of pH 6.5 wasused in the step (C) of Example 1. (Since the same readily degradableresin composition as Example B-1 was used, the active pH range was thesame, namely, pH 5.0 to pH 7.2.)

(Example B-4)

Example B-4 was conducted in the same manner as in the step (c) ofExample B-1, except that distilled water was used instead of thephosphate buffer solution and that 22.5 mg of calcium carbonate (WakoPure Chemical Industries, Ltd.) was added as the neutralizing agent.(Since the same readily degradable resin composition as that of ExampleB-1 was used, the active pH range was the same, namely, pH 5.0 to pH7.2.) The final pH was 6.5.

(Comparative Example B-1)

Comparative Example B-1 was conducted under the same conditions as thoseemployed in Example B-1, except that a 60 mM phosphate buffer solutionof pH 9 was used in the step (C) of Example B-1. (Since the same readilydegradable resin composition as Example B-1 was used, the active pHrange was the same, namely, pH 5.0 to pH 7.2.)

(Comparative Example B-2)

Comparative Example B-2 was conducted under the same conditions as thoseemployed in Example 1, except that a 60 mM phosphate buffer solution ofpH 8.0 was used in the step (C) of Example B-1. (Since the same readilydegradable resin composition as Example B-1 was used, the active pHrange was the same, namely, pH 5.0 to pH 7.2.)

(Comparative Example B-3)

Into 10 ml of a 60 mM phosphate buffer solution of pH 6.5 prepared as adegradation liquid by adding 12 μl of the pro K enzyme solution, thereadily degradable resin composition film cut into 2 cm×2 cm (weight: 45mg) was immersed, and the mixture was shaken at 37° C. and 100 rpm for 7days. The enzyme solution was not replaced. (Since the same readilydegradable resin composition as Example B-1 was used, the active pHrange was the same, namely, pH 5.0 to pH 7.2.)

(Comparative Example B-4)

Comparative Example B-4 was conducted under the same conditions as thoseemployed in Example 1, except that a 60 mM phosphate buffer solution ofpH 4.7 was used in the step (C) of Example B-1. (Since the same readilydegradable resin composition as Example B-1 was used, the active pHrange was the same, namely, pH 5.0 to pH 7.2.)

FIG. 7 shows the fluctuation in pH in Examples B-1 to 4 and ComparativeExamples B-1 to 4. In addition, the following Table 6 shows the resultsof degradation of the readily degradable resin composition.

TABLE 6 at the beginning of acid amount of weight reduction aliphaticthe degradation of catalyst (mg) replacement of polyester temperatureenzyme initial enzyme activity effect after 2 after 4 after 7degradation B′ (° C.) solution pH (pH 5.0 to 7.2) (pH <8.0) days daysdays liquid Example B-1 PEOx 37 pro K 12 7.2 ∘ ∘ 2.84 9.06 21.96 yes μlExample B-2 PEOx 37 pro K 12 7 ∘ ∘ 2.77 9.66 21.18 yes μl Example B-3PEOx 37 pro K 12 6.5 ∘ ∘ 4.42 15.07 disappear yes μl Example B-4 PEOx 37pro K 12 7.2 ∘ ∘ 23.03 disappear disappear no (with μl neutralizingagent) Comparative PEOx 37 pro K 12 9 x x 1.92 5.58 12 yes Example B-1μl Comparative PEOx 37 pro K 12 8 ∘ x 0 3.06 10.13 yes Example B-2 μlComparative PEOx 37 pro K 12 6.5 ∘ ∘ 14.03 15.78 18.62 no (final pHExample B-3 μl 4.2) Comparative PEOx 37 pro K 12 4.7 x ∘ 2.98 4.03 4.79yes Example B-4 μl

Cases where the pH of the degradation liquid was always within the pHrange of 5 to 7.2 in which the enzyme was active during the degradationprocess are represented by O, and other cases are represented by x.

As for the acid catalyst effect, items with pH 8 or less are representedby O, and items with pH 8 or more are represented by x.

(Example B-5) (a) Measurement of Enzyme Activity of Lipase CS2 onBiodegradable Film (Simple Polymer of Aliphatic Polyester (A))

Into each of 60 mM phosphate buffer solutions (11 kinds in a pH range of3.0 to 8.0) which were each 10 ml in volume, and which were prepared asdegradation liquids by adding 48 μl of the CLE enzyme solution thereto,the polylactic acid film (having a thickness of 100 μm) cut into 2 cm×2cm (45 mg) was immersed, and the mixture was shaken at 37° C. and 100rpm for 4 days. The degradation amount (mg) after 4 days was employed asa film degradation activity value. Here, the degradation amount after 4days was a value represented as follows: the film weight (mg) at thebeginning of the degradation−the film weight (mg) after 4 days. Inaddition, for the film weight measurement, values obtained bymeasurement after drying the film in a dryer at 45° C. overnight wereemployed. The film degradation activities in the phosphate buffersolutions of the various pHs were as follows.

TABLE 7 pH 3.0 3.7 4.7 5.5 6.0 6.5 7.0 7.2 7.5 7.8 8.0 activity 0 1 6.056.13 9.33 9 15.08 14.48 12.78 9.73 0.11

(b) Specifying Active pH Range

As can be seen from Table 3 above and FIG. 8 in which the contentsthereof are illustrated, the maximum activity value of lipase CS2 on thepolylactic acid film was 15 which was obtained when the 60 mM phosphatebuffer solution of pH 7.0 was used. A range of pH 4.4 to pH 7.8 in whichthe activity value was not less than 4.5, which was not less than 30% ofthe maximum activity value, was determined as the active pH range foruse of lipase CS2.

(c) Degradation of Readily Degradable Resin Composition (ResinComposition Containing Aliphatic Polyester (A) and Aliphatic Polyester(B′))

Into each of 60 mM phosphate buffer solutions of pH 7.0 which were each10 ml in volume, and which were prepared as degradation liquids byadding 48 μl of the CLE enzyme solution thereto, the readily degradableresin composition film {containing the PEOx as the aliphatic polyester(B′)} cut into 2 cm×2 cm (weight: 45 mg) was immersed, and the mixturewas shaken at 37° C. and 100 rpm for 7 days. To avoid a decrease in pH,the 7 days was divided into 2 days, 2 days, and 3 days, between whichthe degradation liquid was replaced.

(Example B-6)

Example B-6 was conducted under the same conditions as those employed inExample B-5, except that a 60 mM phosphate buffer solution of pH 6.5 wasused in the step (C) of Example B-5. (Since the same readily degradableresin composition as Example B-5 was used, the active pH range was thesame, namely, pH 4.4 to pH 7.8.)

(Example B-7)

Example B-7 was conducted under the same conditions as those employed inExample B-5, except that a 60 mM phosphate buffer solution of pH 7.5 wasused in the step (C) of Example B-5 (Since the same readily degradableresin composition as Example B-5 was used, the active pH range was thesame, namely, pH 4.4 to pH 7.8.)

(Example B-8)

Example B-8 was conducted in the same manner as Example 5, except thatthe readily degradable resin composition film {containing the PEOx 20 asthe aliphatic polyester (B′)} was used instead, and that the temperaturewas changed to 45° C. The initial pH was 7, and the final pH was 4.5,indicating that the degradation was carried out within the active pHrange.

(Comparative Example B-5)

Comparative Example B-5 was conducted under the same conditions as thoseemployed in Example B-5, except that a 60 mM phosphate buffer solutionof pH 8 was used in the step (C) of Example 5. (Since the same readilydegradable resin composition as Example B-5 was used, the active pHrange was the same, namely, pH 4.4 to pH 7.8.)

(Comparative Example B-6)

Comparative Example B-6 was conducted under the same conditions as thoseemployed in Example B-5, except that a 60 mM phosphate buffer solutionof pH 9 was used in the step (C) of Example B-5. (Since the same readilydegradable resin composition as Example B-5 was used, the active pHrange was the same, namely, pH 4.4 to pH 7.8.)

(Comparative Example B-7)

Comparative Example B-7 was conducted under the same conditions as thoseemployed in Example B-5, except that a 60 mM phosphate buffer solutionof pH 4.7 was used in the step (C) of Example B-5. (Since the samereadily degradable resin composition as Example B-5 was used, the activepH range was the same, namely, pH 4.4 to pH 7.8.)

(Comparative Example B-8)

Comparative Example B-8 was conducted under the same conditions as thoseemployed in Example B-5, except that a 60 mM phosphate buffer solutionof pH 3.7 was used in the step (C) of Example B-5. (Since the samereadily degradable resin composition as Example B-5 was used, the activepH range was the same, namely, pH 4.4 to pH 7.8.)

(Comparative Example B-9)

Comparative Example B-9 was conducted under the same conditions as thoseemployed in Example B-5, except that a 60 mM phosphate buffer solutionof pH 3.0 was used in the step (C) of Example B-5. (Since the samereadily degradable resin composition as Example B-5 was used, the activepH range was the same, namely, pH 4.4 to pH 7.8.)

(Comparative Example B-10)

Comparative Example B-10 was conducted in the same manner as Example 5,except that the readily degradable resin composition film {containingthe PEOx 20 as the aliphatic polyester (B′)} was used instead. Theinitial pH was 7, and the final pH was 5.1, indicating that thedegradation was carried out within the active pH range.

FIG. 9 shows the fluctuation in pH in Examples B-5 to 7 and ComparativeExamples B-5 to 9. In addition, the following Table 8 shows the resultsof degradation of the readily degradable resin composition.

TABLE 8 at the beginning of acid amount of weight reduction aliphaticthe degradation of catalyst (mg) replacement of polyester temperatureenzyme initial enzyme activity effect after 2 after 4 after 7degradation B′ (° C.) solution pH (pH 4.4 to 7.8) (pH <8.0) days daysdays liquid Example B-5 PEOx 37 CLE 48 7 ∘ ∘ 18.87 38.13 disappear yesμl (within 7 days) Example B-6 PEOx 37 CLE 48 6.5 ∘ ∘ 24.72 29.35disappear yes μl (within 7 days) Example B-7 PEOx 37 CLE 48 7.5 ∘ ∘15.26 37.64 disappear yes μl (within 7 days) Example B-8 PEOx 20 45 CLE48 7 ∘ ∘ 27.5 disappear yes μl Comparative PEOx 37 CLE 48 8 x x 3.2315.14 36.89 yes Example B-5 μl Comparative PEOx 37 CLE 48 9 x x 0.240.96 1.48 yes Example B-6 μl Comparative PEOx 37 CLE 48 4.7 ∘ ∘ 7.3413.94 19.44 yes (pH 3.8 to Example B-7 μl 4.7) Comparative PEOx 37 CLE48 3.7 x ∘ 4.29 6.1 8.91 yes Example B-8 μl Comparative PEOx 37 CLE 48 3x ∘ 3.05 2.75 3.51 yes Example B-9 μl Comparative PEOx 20 37 CLE 48 7 ∘∘ 5.83 20.04 disappear yes Example B-10 μl (within 7 days)

Cases where the pH of the degradation liquid was always within the pHrange of 4.4 to 7.8 in which the enzyme was active during thedegradation process are represented by O, and other cases arerepresented by x.

As for the acid catalyst effect, items with pH 8 or less are representedby O, and items with pH 8 or more are represented by x.

3. Examples C-1 to 5 and Comparative Examples C-1 to 4 were conducted asfollows.

The enzyme reaction liquids of degradation enzymes used were prepared asfollows.

Pro K (Proteinase K) enzyme reaction liquid

A pro K (Proteinase K) enzyme reaction liquid was prepared by dissolving20 mg of a powder of Tritirachium album-derived Proteinase K(manufactured by Wako Pure Chemical Industries, Ltd.) in 1 ml of a 0.05M Tris-HCl buffer solution (pH 8.0) containing 50w/w % of glycerin.

CLE enzyme reaction liquid

A Cryptococcus sp. S-2-derived lipase CS2 (Japanese Patent ApplicationPublication No. 2004-73123) enzyme reaction liquid having a lipaseactivity of 653 U/mL and provided by National Research Institute ofBrewing was used. The lipase activity was measured by using para-nitrophenyl laurate as the substrate. Here, 1 U of the lipase activity isdefined as the amount of enzyme with which para-nitrophenol is liberatedfrom para-nitro phenyl laurate at 1 μmol/min.

(Measurement of Glass Transition Temperature)

The glass transition temperature (Tg) was measured by using DSC 6220manufactured by Seiko Instruments Inc. (differential scanningcalorimetry). As for measurement conditions, the measurement wasconducted in a nitrogen atmosphere at a rate of temperature rise of 10°C./min from 0 to 200° C. The samples used were PEOx and PEOx 20 to bedescribed later, and the amount of each sample was 5 to 10 mg.

Synthesis of Polyethylene Oxalate (PEOx) (Aliphatic Polyester (B′))

Into a 300-mL separable flask equipped with a mantle heater, a stirrer,a nitrogen inlet, and a condenser, 354 g (3.0 mol) of dimethyl oxalate,223.5 g (3.6 mol) of ethylene glycol, and 0.30 g of tetrabutyl titanatewere introduced. The flask was heated under nitrogen stream from 110° C.until the inside temperature reached 170° C., while methanol was beingdistilled off. Then, the reaction was conducted for 9 hours. At the end,210 ml of methanol was distilled off. Thereafter, stirring was performedfor 1 hour at an inside pressure of 150° C. and at a reduced pressure of0.1 to 0.5 mmHg. After a 7-hour reaction at an inside temperature of170° C. to 190 ° C., the viscosity increased, and the product was takenout. The η inh of the synthesized product was 0.12.

The solution viscosity (η inh) was measured as follows. Specifically,the synthesized polyethylene oxalate which had been vacuum-dried at 120°C. overnight was used. The polyethylene oxalate was immersed in amixture solvent of m-chlorophenol/1,2,4-trichlorobenzene=4/1 (weightratio), and dissolved thereinto at 150° C. in approximately 10 minutesto prepare a solution at a concentration of 0.4 g/dl. Thereafter, thesolution viscosity was measured at 30° C. by use of an Ubbelohdeviscometer (Unit: dl/g).

In addition, the pH of an aqueous solution obtained by dissolving oxalicacid, which was the monomer of the above-described polyethylene oxalate,at a concentration of 0.005 g/ml was 1.6.

Synthesis of polyoxalate (PEOx 20))

Polyoxalate (PEOx 20) was synthesized in the same manner as in theabove-described synthesis of PEOx, except that 94.5 g (0.8 mol) ofdimethyl oxalate and 38.8 g (0.2 mol) of dimethyl terephthalate wereused instead of 354 g (3.0 mol) of dimethyl oxalate.

GPC measurement showed that the weight average molecular weight (Mw) was20000. The GPC used was HLC-8120 manufactured by Tosoh Corporation, andthe columns used were two TSK gel Super HM-H columns, and the guardcolumn used was a TSK guard column Super H-H column. The temperature ofa column oven was set to 40° C. Chloroform was used as an eluent, andthe flow rate was set to 0.5 ml/min. The amount of sample injected was15 μl. Polystyrene dissolved in chloroform was used as a standard. Asfor sample preparation, chloroform was used as a solvent with a sampleconcentration of 5 mg/ml, and the sample was filtered before use.

(Properties of PEOx and PEOx 20)

The monomer, oxalic acid, shows a pH of 1.6 at a concentration of 0.005g/ml. The PEOx and the PEOx 20 release, upon hydrolysis, oxalic acid oroxalic acid oligomers in an aqueous solution.

Monomer Content and Glass Transition Temperature of Polyoxalate

dimethyl terephthalic oxalate acid ethylene glycol Tg (mol) (mol) (mol)(° C.) PEOx 3 0 3.6 25 PEOx 20 0.8 0.2 1.2 45

Fabrication of Readily Degradable Resin Composition Film (AliphaticPolyester (A)+Aliphatic Polyester (B′))

Master pellets of polylactic acid (4032D manufactured by NatureWorksLLC)/PEOx or PEOx 20=95/5 mass % were melt blended by using a twin-screwextruder (manufactured by TECHNOVEL CORPORATION) at 200° C. Then,readily degradable resin composition films of 100 μm and of 250 μm wereformed by using Labo Plastomill (manufactured by Toyo Seiki Seisaku-sho,Ltd.).

Specifying Active pH Range of Protease K (a) Measurement of EnzymeActivity of Protease K on Biodegradable Film (Simple Polymer ofAliphatic Polyester (A) Component)

Into each of 60 mM phosphate buffer solutions (11 kinds in a pH range of4.7 to 9.0) which were each 10 ml in volume, and which were prepared asdegradation liquids by adding 12 μl of the pro K enzyme solutionthereto, the polylactic acid film (having a thickness of 100 μm) cutinto 2 cm×2 cm (45 mg) was immersed, and the mixture was shaken at 37°C. and 100 rpm for 4 days. The degradation amount (mg) after 4 days wasemployed as a film degradation activity value. Here, the degradationamount after 4 days was a value represented as follows: the film weight(mg) at the beginning of the degradation−the film weight (mg) after 4days. In addition, for the film weight measurement, values obtained bymeasurement after drying the film in a dryer at 45° C. overnight wereemployed. The film degradation activities in the phosphate buffersolutions of the various pHs were as follows.

TABLE 9 pH 4.7 5.5 6.0 6.5 7.0 7.2 7.5 7.8 8.0 8.5 9.0 activity 1.6 5.099.13 7.15 3.59 3.15 2.34 2.33 2.57 2.21 2.08

(b) Specifying Active pH Range of Protease K

As can be seen from the above-described Table 1 and FIG. 10 in which thecontents thereof are illustrated, the maximum activity value of proteaseK on the polylactic acid film was 9.13 which was obtained when the 60 mMphosphate buffer solution of pH 6.0 was used. A range of pH 5.0 to pH7.2 in which the activity value was not less than 2.7, which was notless than 30% of the maximum activity value, was determined as theactive pH range for use of protease K.

Specifying Active pH Range of Lipase CS2 (a) Measurement of EnzymeActivity of Lipase CS2 on Biodegradable Film (Simple Polymer ofAliphatic Polyester (A))

Into each of 60 mM phosphate buffer solutions (11 kinds in a pH range of3.0 to 8.0) which were each 10 ml in volume, and which were prepared asdegradation liquids by adding 48 μl of the CLE enzyme solution thereto,the polylactic acid film (having a thickness of 100 μm) cut into 2 cm×2cm (45 mg) was immersed, and the mixture was shaken at 37° C. and 100rpm for 4 days. The degradation amount (mg) after 4 days was employed asa film degradation activity value. Here, the degradation amount after 4days was a value represented as follows: the film weight (mg) at thebeginning of the degradation−the film weight (mg) after 4 days. Inaddition, for the film weight measurement, values obtained bymeasurement after drying the film in a dryer at 45° C. overnight wereemployed. The film degradation activities in the phosphate buffersolutions of the various pHs were as follows.

TABLE 10 pH 3.0 3.7 4.7 5.5 6.0 6.5 7.0 7.2 7.5 7.8 8.0 activity 0 16.05 6.13 9.33 9 15.08 14.48 12.78 9.73 0.11

(b) Specifying Active pH Range of Lipase CS2

As can be seen from the above-described Table 2 and FIG. 11 in which thecontents thereof are illustrated, the maximum activity value of LipaseCS2 on the polylactic acid film was 15 which was obtained when the 60 mMphosphate buffer solution of pH 7.0 was used. A range of pH 4.4 to pH7.8 in which the activity value was not less than 4.5, which was notless than 30% of the maximum activity value, was determined as theactive pH range for use of Lipase CS2.

(Example C-1)

Into a 50-ml Falcon tube, the readily degradable resin composition film(in which the PEOx was used as the aliphatic polyester B′) cut into 2cm×2 cm (90 mg in weight and 250 μm in thickness), 30 ml of distilledwater (neutral) were added. Moreover, 36 μl of the pro K enzyme solutionand calcium carbonate (manufactured by Wako Pure Chemical Industries,Ltd., particle diameter: 10 to 15 μm) in an amount of 0.5 times the filmweight were added thereto. The reaction was conducted at 37° C. and 200rpm for one week.

(Example C-2)

Into a 3-L water bath equipped with a temperature controller, a heater,and a stirrer, the readily degradable resin composition films (20sheets, total weight: 12 g, thickness: 250 μm) cut into 5 cm×5 cm, and 3L of distilled water (neutral) were introduced. Moreover, 15 ml of theCLE enzyme solution, and chitosan (chitosan 50 manufactured by Wako PureChemical Industries, Ltd., particle diameter: 30 to 300 μm) in an amountof 1.5 times the film weight were added thereto. The reaction wasconducted at 37° C. and 500 rpm for one week.

(Example C-3)

Example C-3 was conducted in the same manner as in Example C-2, exceptthat chitosan was replaced with calcium carbonate.

(Example C-4)

Into a 25-ml glass vial, the readily degradable resin composition film(in which the PEOx 20 was used as the aliphatic polyester B′) cut into 2cm×2 cm (70 mg in weight and 150 μm in thickness), 10 ml of distilledwater (neutral) were added. Moreover, 48 μl of the CLE enzyme solutionand calcium carbonate (manufactured by Wako Pure Chemical Industries,Ltd., particle diameter: 10 to 15 μm) in an amount of 0.5 times the filmweight were added thereto. The reaction was conducted at 45° C. and 100rpm for one week.

(Comparative Example C-1)

Comparative Example C-1 was conducted in the same manner as in ExampleC-1, except that no calcium carbonate was added.

(Comparative Example C-2)

Comparative Example C-2 was conducted in the same manner as in ExampleC-3, except that no calcium carbonate was added.

(Comparative Example C-3)

Comparative Example C-3 was conducted in the same manner as in Example4, except that the degradation temperature was changed to 37° C.

TABLE 11 amount of weight reduction (reduction percentage) aliphatictemperature enzyme neutralizing film initial final after 2 after 4 after7 polyester B′ (° C.) solution agent weight pH pH days days days ExampleC-1 PEOx 37 pro K calcium 90 mg 7.16 6.65 28.96 mg 52.79 mg 77.05 mgcarbonate (−32.2%) (−58.7%) (−85.6%) Example C-2 PEOx 37 CLE chitosan 12g 6.3 5.2 — — 5.12 g (−42.7%) Example C-3 PEOx 37 CLE calcium 12 g 7.56.5 — — 4.56 g carbonate (−38.0%) Example C-4 PEOx 20 45 CLE calcium 70mg 7.16 6 68.14 mg disappear carbonate (−97.3%) Comparative PEOx 37 proK none 90 mg 7.0 3.6 0  0.43 mg 1.74 mg Example C-1   (−0%)  (−0.5%) (−1.9%) Comparative PEOx 37 CLE none 12 g 7.0 4.93 — — 0.57 g ExampleC-2  (−4.8%) Comparative PEOx 20 37 CLE calcium 70 mg 7.16 6.7 23.11 mg43.61 mg 62.71 mg Example C-3 carbonate   (−33%) (−62.3%) (−89.6%)

From the results of Examples C-1 to 3 and Comparative Examples C-1 and2, it was found that when the acid neutralizing agent was added to thedegradation liquid, the degradation amount increased because thedecrease in pH was successfully inhibited, and thus the enzyme activitywas maintained. In addition, from the results of Example 4 andComparative Example 3, it was found that the degradation amountincreased by setting the degradation temperature to a value not lowerthan the glass transition temperature of the aliphatic polyester B′.

Next, the following experiments were carried out to examine thedegradation performances with an acid neutralizing agent incompatiblewith water and with an acid neutralizing agent compatible with water.

(Example C-5)

Into a 25-ml glass vial, the readily degradable resin composition filmcut into 2 cm×2 cm (45 mg in weight and 100 μm in thickness), 10 ml ofdistilled water (neutral) were added. Moreover, 12 μl of the pro Kenzyme solution and calcium carbonate in an amount of 0.5 times the filmweight were added thereto. The reaction was conducted at 37° C. and 100rpm for one week.

(Comparative Example C-4)

Into a 25-ml vial, the readily degradable resin composition film cutinto 2 cm×2 cm (weight: 45 mg, thickness: 100 μm) and a degradationliquid (pH: 7.0, 10 ml of the phosphate buffer solution and 12 μl of thepro K enzyme solution) were added. The reaction was conducted at 37° C.and 100 rpm for one week, and the degradation liquid was replaced atintervals of 2 days, 2 days, and 3 days.

TABLE 12 amount of weight reduction (reduction percentage) aliphatictemperature enzyme neutralizing film initial final after 2 after 4 after7 polyester B′ (° C.) solution agent weight pH pH days days days ExampleC-5 PEOx 37 pro K calcium 45 mg 7.16 6.5 23.03 mg disappear disappearcarbonate (−51.2%) (4 days) (4 days)  (−100%)  (−100%) Comparative PEOx37 pro K (60 mM 45 mg 7.2 6.85  2.84 mg 9.06 mg 21.96 mg Example C-4phosphate  (−6.3%) (−20.1%) (−47.1%) buffer solution)

These results indicated that when a comparison was made between the acidneutralizing agent incompatible with water and the acid neutralizingagent compatible with water, the acid neutralizing agent incompatiblewith water acted more effectively. This indicated that the compatibleacid neutralizing agent of Comparative Example C-3 entered the inside ofthe readily degradable resin composition, and neutralized the acid, sothat the degradation performances were deteriorated.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a photograph in which the transparency is comparedbetween Example A-1 (left) and Comparative Example A-14 (right).

[FIG. 2] FIG. 2 is an HPLC chart of Example A-3.

[FIG. 3] FIG. 3 is a graph showing a correlation between the degradationpercentage after a 4-day degradation test and the SP value.

[FIG. 4] FIG. 4 is a graph showing FT-IR of a white turbid substance.

[FIG. 5] FIG. 5 is a graph showing HPLC measurement conditions.

[FIG. 6] FIG. 6 shows degradation activity of pro K on polylactic acidfilm.

[FIG. 7] FIG. 7 shows change with time in pH in a case where a readilydegradable resin composition was degraded in an enzyme solution of proK.

[FIG. 8] FIG. 8 shows a degradation activity of CLE on polylactic acidfilm.

[FIG. 9] FIG. 9 shows change with time in pH in a case where a readilydegradable resin composition was degraded in an enzyme solution of CLE.

[FIG. 10] FIG. 10 shows degradation activity of pro K on polylactic acidfilm.

[FIG. 11] FIG. 11 shows degradation activity of CLE on polylactic acidfilm.

1. A method for producing an oligomer and/or a monomer, comprisingdegrading a biodegradable resin in a degradation liquid containing abiodegradation enzyme, a buffer agent, an organic solvent, and water,wherein the organic solvent has an SP value of less than 8.5 or morethan 11.5, and a percentage content (by volume) of the organic solventin the degradation liquid is higher than 1% and lower than 15%.
 2. Theproduction method according to claim 1, wherein the organic solvent isethanol.
 3. The production method according to claim 1, wherein thebiodegradable resin contains a degradation accelerator.
 4. Theproduction method according to claim 3, wherein a degradationtemperature in the production method is a temperature 5° C. lower than aglass transition temperature of the degradation accelerator, or higher.5. The production method according to claim 3, wherein the degradationaccelerator releases an acid upon hydrolysis.
 6. The production methodaccording to claim 5, wherein the biodegradable resin is a readilydegradable resin composition comprising: an aliphatic polyester (A)which is biodegradable; and an aliphatic polyester (B′) which releasesan acid upon hydrolysis, and which is biodegradable at a higherdegradation rate than that of the aliphatic polyester (A).
 7. Theproduction method according to claim 3, wherein the degradationaccelerator is a polyoxalate.
 8. The production method according toclaim 1, wherein the biodegradable resin is a polylactic acid resin. 9.A method for degrading a readily degradable resin composition comprisingan aliphatic polyester (A) which is biodegradable, and an aliphaticpolyester (B′) which releases an acid upon hydrolysis and which isbiodegradable at a higher degradation rate than that of the aliphaticpolyester (A), the method comprising: (a) specifying a maximum activitypH value at which a degradation activity value of a hydrolase, when usedto degrade a simple polymer of the aliphatic polyester (A) alone in abuffer solution, is maximized; (b) a step of determining an active pHrange in which the degradation activity value is not less than 30% ofthe degradation activity value at the maximum activity pH value; and (c)a step of degrading the readily degradable resin composition in anenzyme reaction liquid containing the hydrolase, and having a pH whichis within the active pH range and which is less than 8.0, wherein the pHof the enzyme reaction liquid is maintained within the active pH rangeand at less than 8.0 in the degradation step.
 10. A method for degradinga readily degradable resin composition comprising an aliphatic polyester(A) which is biodegradable, and an aliphatic polyester (B′) whichreleases an acid upon hydrolysis and which is biodegradable at a higherdegradation rate than that of the aliphatic polyester (A), the methodcomprising degrading the readily degradable resin composition in anenzyme reaction liquid containing a degradation enzyme, and an acidneutralizing agent incompatible with the enzyme reaction liquid.
 11. Thedegradation method according to claim 10, wherein during the enzymereaction, the pH of the enzyme reaction liquid is maintained within anactive pH range determined by the following steps (a′) to (b′) and atless than 8.0: (a′) specifying a maximum activity pH value at which adegradation activity value of the degradation enzyme, when used todegrade a simple polymer of the aliphatic polyester (A) alone in abuffer solution, is maximized; and (b′) a step of determining an activepH range in which the degradation activity value is not less than 30% ofthe degradation activity value at the maximum activity pH value.
 12. Thedegradation method according to claim 10, wherein the acid neutralizingagent is calcium carbonate or chitosan.
 13. The degradation methodaccording to claim 9, wherein a degradation temperature is a temperature5° C. lower than a glass transition temperature of the aliphaticpolyester (B′), or higher.
 14. The degradation method according to claim9, wherein the hydrolase is protease, lipase, cellulase, or cutinase.15. The degradation method according to claim 9, wherein the acidreleased from the aliphatic polyester (B′) is oxalic acid or maleicacid.
 16. The degradation method according to claim 9, wherein thereadily degradable resin composition is one which is obtained bydispersing a polyoxalate in a polylactic acid-based resin.
 17. Adegradation liquid for degrading a readily degradable resin compositioncomprising an aliphatic polyester (A) which is biodegradable, and analiphatic polyester (B′) which releases an acid upon hydrolysis andwhich is biodegradable at a higher degradation rate than that of thealiphatic polyester (A), wherein the degradation liquid is a liquidmixture containing a degradation enzyme, and an acid neutralizing agentincompatible with an enzyme reaction liquid.
 18. The degradation liquidaccording to claim 17, wherein the acid neutralizing agent is calciumcarbonate or chitosan.
 19. The degradation liquid according to claim 17,wherein a hydrolase is protease, cutinase, cellulase, or lipase.